Effect of calcium peroxide on the water quality and bacterium community of sediment in black-odor water

Accepted Manuscript Effect of calcium peroxide on the water quality and bacterium community of sediment in black-odor water Wen-Huai Wang, Yi Wang, Pan Fan, Lin-Feng Chen, Bao-Hua Chai, Jing-Chan Zhao, Lu-Qin Sun PII:

S0269-7491(18)34120-4

DOI:

https://doi.org/10.1016/j.envpol.2018.11.069

Reference:

ENPO 11896

To appear in:

Environmental Pollution

Received Date: 10 September 2018 Revised Date:

5 November 2018

Accepted Date: 22 November 2018

Please cite this article as: Wang, W.-H., Wang, Y., Fan, P., Chen, L.-F., Chai, B.-H., Zhao, J.-C., Sun, L.-Q., Effect of calcium peroxide on the water quality and bacterium community of sediment in blackodor water, Environmental Pollution (2018), doi: https://doi.org/10.1016/j.envpol.2018.11.069. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Effect of calcium peroxide on the water quality and bacterium

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community of sediment in black-odor water

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Wen-Huai Wang a, Yi Wang a*, Pan Fan a, Lin-Feng Chen a, Bao-Hua Chai a, Jing-Chan Zhao b,

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Lu-Qin Sun c

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a

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Technology, China

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b

College of Chemistry & Materials Science, Northwest University, Xi'an, 710069, China

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Environmental Science Department, University of San Francisco, California, CA 94117, USA

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ABSTRACT:

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School of Environmental and Municipal Engineering, Xi’an University of Architecture and

This study investigated how efficiently CaO2 could treat black-odor landscape

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water caused by low dissolved oxygen (DO) in a field experiment of 600 m2. The

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study demonstrated that CaO2 could significantly elevate the DO concentration in

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waters and the oxidation–reduction potential (ORP) level in sediments (p=0.003 and

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p=0), which is conducive to improving the anoxic environment of landscape water.

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The concentrations of total chemical oxygen demand (TCOD) and S2− in overlying

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and interstitial waters were considerably decreased. The average concentrations of

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TCOD in the overlying and interstitial waters of the test zone (TZ) were 52.98% and

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66.05% of those of the control zone (CZ), and the average concentrations of S2− in the

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overlying and interstitial waters of TZ were 29.63% and 39.79% of those of CZ.

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Meanwhile, CaO2 could obviously reduce turbidity but increase the transparency in

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the overlying water. The mean value of turbidity in the overlying water of TZ was

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39.46% of that of CZ, whereas the transparency in the overlying water of TZ was 2.07

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ACCEPTED MANUSCRIPT times that of CZ. Furthermore, CaO2 changed the microbial community structure in

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the sediments, where the relative abundance of anaerobic bacteria was decreased but

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that of the aerobic bacteria was increased with some functional bacteria. In summary,

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CaO2 could significantly increase the DO and ORP in black-odor landscape water,

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obviously inhibit the release of pollutants from sediment, and increase the diversity of

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microbial strains. Consequently, the black-odor phenomenon of landscape water could

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be alleviated effectively by adding CaO2.

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Capsule:

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This paper could provide an effective reference for the management of

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black-odor landscape water and demonstrate an important field case for similar

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problems.

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Keywords: Calcium peroxide; Landscape water; Sediment release; Black-odor

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governance; Microbial flora

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1. Introduction

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Urban landscape water has an important ecological value in improving local

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climate and beautifying urban environment (Mcgoff et al., 2017). Nevertheless, this

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type of water is seriously polluted by area-source pollution because it is commonly

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located in urban districts with large population density (Wang et al., 2018).

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Meanwhile, a large amount of pollutants are gradually accumulated in the sediments

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of rivers and lakes in the form of endogenous pollutant due to the defects of landscape

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water, such as shallow water, poor fluidity, and weak self-purification capacity (Ao et

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al., 2018). In summer, higher temperature contributes to the higher microbial

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ACCEPTED MANUSCRIPT metabolisms which will convert the water environment to anoxic or anaerobic

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conditions due to the rapid consumption of dissolved oxygen (DO) in the water. The

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proliferation, growth, and metabolism of anaerobic bacteria are accompanied with the

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corruption, decomposition, fermentation, and transformation of organic compounds in

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sediments (Li et al., 2016), which strengthen the production of substances, such as

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ammonia nitrogen (NH4+–N), humus, hydrogen sulfide, methane, and mercaptan.

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Among these substances, ammonia (NH3), hydrogen sulfide, and mercaptan inevitably

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diffuse and spread out into the surroundings, which are probably the main reasons

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turn the water into smelly or olfactory water. Meanwhile, some metals, such as iron

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and manganese, are reduced in the anoxic environment and further combined with S2−

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to form ferrous sulfide and other compounds (Ololade et al., 2016), which usually

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cause the water turning into black color in the landscape water due to a large quantity

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of negative colloids (FeS and MnS) being adsorbed by suspended particles and floated

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in the overlying water. The formation of black and smelly water body will not only

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reduces the aesthetic value of landscape water but also harms the ecological balance

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and introduces many hygienic problems (Andreasen et al., 2013; Shen et al., 2014). A

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total of 1861 water bodies (85.7% of rivers and 14.3% of lakes) in China were labeled

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as black-odor water by the end of February 2017. Thus, how to deal and treat

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black-odor landscape water is a common and serious issue existing in China.

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The popular treatments used today to restore black-odor landscape water are

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physical methods (e.g., sediments dredging, sediments coverage, and artificial

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aeration) (Richardson et al., 2011), chemical methods (e.g., addition of aluminum salt, 3

ACCEPTED MANUSCRIPT sodium nitrate, calcium nitrate, and hydrogen peroxide) (Ronen et al., 2010), and

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biological methods (e.g., purification of aquatic plants, microorganism strengthening,

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and exogenous microorganism delivery) (Faccioabbba, 2012). These techniques can

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accordingly improve the quality of black-odor landscape water but have some obvious

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defects in their applications. Physical methods are often companied with the issues of

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high cost, low efficiency, and secondary pollution. For example, the sediments after

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dredging out from the bottom need to be properly further treated, and more pollutants

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could be released into the water from sediments by artificial aeration (Wang et al.,

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2017b; Uggetti et al., 2016). While using chemical methods dealing with the

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black-odor water have many problems too, such as, applying aluminum salt is

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commonly known to be toxic to aquatic organisms (Freitas et al., 2016), using nitrate

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would increase the concentration of nitrate nitrogen in the overlying water (Liu et al.,

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2016; Bindhu et al., 2016), Na2CO4 has a short timeliness, therefore is easily soluble

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in water and moist atmosphere (Sindelar et al., 2014), and the use of hydrogen

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peroxide is dangerous and unstable (Zingaretti et al., 2016). Biological methods are

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usually commented as low efficiency, poor stability, and high susceptibility to

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environmental conditions. Therefore, a safer, greener, more economical and efficient

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technology is absolutely needed to solve the black-odor problem of landscape water

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caused by low DO.

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Calcium peroxide (CaO2) can release oxygen molecules slowly in moist air or

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water and it is safe to aquatic ecosystem as a common food additive; thus, CaO2 can

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be used in the in-situ treatment of black-odor landscape water (Lu et al., 2017). 4

ACCEPTED MANUSCRIPT Currently, there are considerable literatures study the effects of CaO2, which mainly

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concentrates on the removal of trichloroethylene in water, degradation of

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endocrine-disrupting compounds in waste activated sludge (Zhang et al., 2015a;

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Zhang et al., 2015b), and reduction in triamcinolone acetonide, benzene, and

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persistent organic pollutants in the environment (Wang et al., 2017a; Zhang et al.,

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2018). However, the effects of CaO2 on black-odor landscape water and the microbial

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community structure in sediments are seldom studied. In this study, CaO2 was applied

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into the severely black-odor landscape water of 600 m2, as a slow-releasing peroxide.

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The feasibility and stability of CaO2 for emergency treatment of black-odor landscape

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water were explored and evaluated and the improvement of anoxic environment in

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water and the change of microbial community structures in sediments were recorded

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and studied. This study is important in managing black-odor landscape water and

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provides a valuable field case for reference in the future.

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2. Materials and methods

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2.1 General situation and design of the experiment

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Xi’an moat surrounds the ancient city wall of Xi’an, and its original function was

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to prevent military attacks. At present, Xi’an moat serves as urban landscape and

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storm-water storage. Xi’an moat has a circumference of 14.8 km, a width of 15–20 m,

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and a depth of 1–8 m. The water velocity in Xi’an moat is extremely small, which

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allows its sediment to reach the depth of 3 meters high.

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The test site of this study is located in a relatively closed zone of the northeast

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corner of Xi’an moat, where the overlying water is 17 meters in width and 1.6 meters 5

ACCEPTED MANUSCRIPT in depth and the sediments are 0.9 meters in depth. The control zone (CZ) and test

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zone (TZ) were set along the direction of water flow in the test site, which were both

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30 meters in length and 10 meters in width. The two zones were naturally separated

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by a platform used as a tourists resting place, which is 15 meters in length and 10

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meters in width. At the beginning of the experiment, 75 kg of CaO2 with a purity of

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76.3% was sprinkled evenly on the surface of sediment in TZ, whereas CZ was in the

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original condition. In addition, five sampling points were selected for both zones (i.e.,

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in the center and four corners), and these sampling points in the same zone were

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studied as a test areas.

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The experiment lasted for 2 months in the summer of 2017. The average water

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temperature of the sampling days was 30.2 °C±0.7 °C during the experiment. At the

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48th and 61st days of the experiment, reservoir water was replenished to the Xi’an

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moat at the upstream 2.5 km of the test site to improve the water quality by the

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Management Committee of Xi’an moat.

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2.2 Sampling

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The overlying water was collected individually using a sampler at 0.5 meters

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below the surface water at five sampling points both in CZ and TZ. The sediment

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samples were grabbed below the surface sediment phase approximately 0.10 meters

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by a gravity sediment collector from five sampling points in the CZ and TZ

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respectively. The supernatant of the sediments sample centrifuged by a refrigeration

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centrifuge (5804R) was obtained as a representative sample of the interstitial water.

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Water and sediment samples were collected at 9:00 am every 7 days. The sediment

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ACCEPTED MANUSCRIPT samples from five sampling points in CZ and TZ were collected and mixed

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respectively as representative samples of each experimental zone to determine the

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microbial community structure for the study site.

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2.3 Analysis of samples

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2.3.1 Analysis of water quality and physicochemical index of sediment

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Temperature (T), transparency, DO, and oxidation–reduction potential (ORP)

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were monitored at the field site, whereas other parameters (e.g., turbidity, S2−, SO42−,

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and total chemical oxygen demand (TCOD)) were tested in the Key Laboratory of the

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Ministry of Education. T, DO, and ORP were measured with a HACH portable

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multifunctional water quality meter (HQ-30d), transparency was metered with a

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Secchi disk, turbidity was analyzed with a spectrophotometer (XINMAO752N), and

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TCOD was detected by potassium dichromate method. S2− was measured by

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dimethyl-aniline spectrophotometry after pretreatment by NaOH–zinc acetate,

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whereas SO42− was analyzed by anion chromatography (ICS 1100).

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2.3.2 Identification of microbial strains in sediment

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High-throughput sequencing of the sediments in CZ and TZ were conducted with

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the Illumina MiSeq system, which contributed to understanding the difference in

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bacterial community structure in both sediments. The specific measurement steps

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are discussed as follows:

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The total DNA was extracted from sediment using the OMEGA kit (Life, USA)

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while its completeness was tested by agarose gel electrophoresis. Genomic DNA was

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accurately quantified using the Qubit 2.0 DNA Assay Kit (Life, USA) to determine 7

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the amount of DNA that should be added to the PCR reaction. PCR was amplified

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with the primers of 341F (5′-CCCTACACGACGCTCTTCCGATCTG-3′) and

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805R (5′-GACTGGAGTTCCTTGGCACCCGAGAATTCCA-3′). The PCR amplification procedure was conducted as follows: pre-denaturation at

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94 °C for 3 min, denaturation at 94 °C for 30 s, annealing at 45 °C for 20 s, extension

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at 65 °C for 30 s, repeating 5 cycles; denaturation at 94 °C for 20 s, annealing at 55 °C

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for 20 s, extension at 72 °C for 30 s, repeating 20 cycles; introduction of Illumina

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bridge PCR compatible primers, pre-denaturation at 95 °C for 30 s, denaturation at

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95 °C for 15 s, annealing at 55 °C for 15 s, extension at 72 °C for 30 s, repeating 5

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cycles.

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2.4 Statistical analysis

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The experimental data were statistically analyzed, calculated, and plotted using

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Origin 9.0 and Excel software. In the strain identification phase, the base sequence

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obtained from high-throughput sequencing was first decontaminated using

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Trimmomatic, and high-quality double-end sequences were connected by the flash

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software to obtain optimized sequences. Sequences were clustered into operational

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taxonomic unit (OTU) at a 97% identity threshold with the using UPARSE software,

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then the OTU representative sequence was compared with the bacterial RDP database

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by using the RDP classifier software to obtain OTU species information. The Mothur,

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R language barplot, and R language pheatmap software packages were used to

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analyze the Alpha diversity of the strains, species richness, and differences in species

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abundance distribution.

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The average value, standard deviation, and variance of the data were analyzed 8

ACCEPTED MANUSCRIPT using SPSS software (PASW Statistics 20.0). The homogeneity of variance among

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samples was tested using f-test method. The means were tested using t-test method

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with a significance level of p < 0.05.

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3. Results

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3.1 Effect of CaO2 on quality of landscape water

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3.1.1 Effect of CaO2 on the overlying water

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1) Time course of turbidity and transparency in the overlying water

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Fig. 1 shows the variations in turbidity and transparency in the overlying water

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of different zones. As shown in the figure, the turbidity in the overlying water of CZ

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increased gradually compared to the initial value, but that of TZ decreased.

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Unsurprisingly, the variation trends of transparency in both zones were opposite to

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those of turbidity.

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Fig. 1 Time course of turbidity and transparency in the overlying water of different zones: (a) turbidity, (b) transparency

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Fig. 1(a) shows that the initial values of turbidity in the overlying water of CZ

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and TZ were 15.26±0.87 and 16.12±0.93 NTU, respectively. The turbidity in the

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overlying water of CZ increased gradually compared to the initial value, and it

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reached the maximum value (23.16±1.07 NTU) at the 43rd day. However, the 9

ACCEPTED MANUSCRIPT turbidity in the overlying water of TZ decreased stably compared to the initial value,

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and it reached the minimum value (4.08±0.36 NTU) at the end of the experiment. As

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shown in Fig. 1(b), the transparency in the overlying water of CZ decreased gradually

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compared to the initial value, and it reached the minimum value (22.2±1.3 cm) at the

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36th day. However, the transparency in the overlying water of TZ increased stably,

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and it reached the maximum value (69.8±1.1 cm) at the 50th day. The average values

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of turbidity in the overlying water of CZ and TZ were 19.92±0.99 and 7.86±0.87

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NTU (p=0), respectively, throughout the test. By contrast, those of transparency were

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29.2±1.9 and 60.5±2.1 cm (p=0). Thus, the mean value of turbidity in the overlying

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water of TZ was 39.46% of that of CZ, whereas the mean value of transparency in the

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overlying water of TZ was 2.07 times that of CZ.

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Therefore, CaO2 could significantly increase the transparency in the overlying

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water of black-odor landscape water but decrease the turbidity. 2) Time course of DO and ORP in the overlying water

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Fig. 2 shows the variations in DO and ORP in the overlying water of both areas.

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As shown in Fig. 2, the DO concentration and ORP level in the overlying water of TZ

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were constantly higher than those of CZ during the experiment.

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As shown in Fig. 2, the initial values of DO concentration and ORP level in the

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overlying water of CZ were similar to those of TZ. The initial DO (2.08±0.05 mg L-1)

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and initial ORP (23.9±2.3 mv) were relatively low in the overlying water of CZ; both

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decreased stably compared to the initial value and reached the minimum value

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(0.13±0.04 mg L-1 and −178.9±7.3 mv) at the 36th and 57th day, respectively. 10

ACCEPTED MANUSCRIPT However, the variation trends of DO and ORP in the overlying water of TZ increased

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gradually first and then reached the maximum value (7.26±0.11 mg L-1 and 83.7±3.6

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mv) at the 8th and 36th days, respectively. The DO concentration and ORP level in

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the overlying water of TZ were constantly higher than those of CZ during the

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experiment although the numbers went down a little bit as time passed. The average

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DO concentrations in the overlying water of TZ and CZ were 4.50±1.12 and

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1.19±1.10 mg L-1 (p=0.003), respectively; the former was 3.78 times the latter. The

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average ORP levels in the overlying water of TZ and CZ were 62.3±3.2 and

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−73.5±6.2 mv (p=0), respectively; the former was significantly higher than the latter.

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Fig. 2 Time course of DO and ORP in the overlying water of different zones: (a) DO, (b) ORP

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Therefore, CaO2 could significantly increase the DO concentration and ORP

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level of the overlying water in the black-odor water body. 3) Time course of TCOD and sulfur concentration in the overlying water

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Fig. 3 shows the variations of TCOD, S2−, and SO42− in the overlying water of

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both zones. As shown in the figure, the concentrations of TCOD and S2− increased

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first and then decreased in the overlying water of CZ, while the concentration of

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SO42− decreased stably compared with the initial value. Nevertheless, the variation 11

ACCEPTED MANUSCRIPT trends of TCOD, S2−, and SO42− in the overlying water of TZ were contrary to those of

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CZ.

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Fig. 3 Time course of TCOD and S concentrations in the overlying water of different zones: −

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(a) TCOD, (b) S2 , and SO42

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Fig. 3(a) shows the variation trends of TCOD concentrations in the overlying

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water for both zones. As shown in the figure, the initial TCOD concentrations in the

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overlying water of CZ and TZ were 68.33±3.52 and 70.05±3.37 mg L-1, respectively.

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These values considerably exceeded the concentration limit of Chinese Surface Water

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Quality Standards for Class V (COD ≤ 40 mg L-1, GB3838-2002). However, the

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TCOD concentration in the overlying water of CZ was constantly higher than that of

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TZ during the entire experiment. TCOD concentration increased gradually and

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reached the maximum value (105.32±4.18 mg L-1) at the 36th day in the overlying

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water of CZ, whereas the concentration decreased gradually and reached the

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minimum value (29.06±2.28 mg L-1) at the 36th day in the overlying water of TZ. The

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average TCOD concentrations in the overlying water of TZ and CZ were 43.78±3.47

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and 82.63±4.32 mg L-1 (p=0), respectively, which indicated that CaO2 could reduce

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47.02% TCOD in the overlying water of TZ compared with that of CZ.

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Fig. 3(b) shows the variation trends of S2− and SO42− concentrations in the 12

ACCEPTED MANUSCRIPT overlying water of different zones. The initial S2− concentrations in the overlying

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water of CZ and TZ were the same (0.13±0.02 mg L-1). The S2− concentration

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increased first and reached the maximum value (0.42±0.03 mg L-1) at the 43rd day in

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the overlying water of CZ, but the concentration decreased steadily (except for the

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end of the experiment) and reached the minimum value (0.03±0.01 mg L-1) at the 50th

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day in the overlying water of TZ. During the entire experiment, the average S2−

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concentrations were 0.27±0.02 and 0.08±0.01 mg L-1 (p=0) in the overlying water of

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CZ and TZ, respectively, which indicated CaO2 could decrease 70.37% S2− in the

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overlying water. The variation trends of SO42− in the overlying water of different

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zones were contrary to those of S2−. The initial SO42− concentrations in the overlying

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water of CZ and TZ were similar, which were 32.26±2.16 and 31.68±1.87 mg L-1,

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respectively. The SO42− concentration decreased uninterruptedly and reached the

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minimum value (23.36±1.72 mg L-1) at the 36th day in the overlying water of CZ, but

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the concentration increased first and then reached the maximum value (92.68±2.82

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mg L-1) at the 43rd day in the overlying water of TZ. The average SO42−

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concentrations were 28.06±1.32 and 70.75±1.87 mg L-1 (p=0) in the overlying water

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of CZ and TZ, respectively; the latter was 2.52 times the former.

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In summary, CaO2 could greatly reduce the concentrations of TCOD and S2− in

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the overlying water of the black-odor landscape water, but it is possible to increase the

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concentration of SO42−. Therefore, CaO2 could reduce sulfur effectively but promote

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sulfur oxidation to a high valence (SO42−).

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3.1.2 Effect of CaO2 on DO concentration of the sediment–water interface 13

ACCEPTED MANUSCRIPT Table 1 shows the variations in DO concentration at the sediment–water interface

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of different zones. As shown in the table, the initial DO concentrations in CZ and TZ

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were the same. The DO concentration at the sediment–water interface of TZ increased

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first, reaching the maximum value (4.02±0.18 mg L-1) at the 22nd day and then

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dropped gradually. The concentration was higher than 1.60 mg L-1 at the

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sediment–water interface of TZ throughout the test (except the starting point).

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However, the DO concentration at the sediment–water interface of CZ was low lesser

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than 0.20 mg L-1 for the entire experiment. Thus, the average DO concentrations were

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2.56±0.11 and 0.08±0.04 mg L-1 (p=0) at the sediment–water interface of CZ and TZ,

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respectively; the former was 32 times the latter.

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Table 1 DO concentration at the sediment–water interface of different zones during the experiment

DO（ （mg L-1）

CZ

TZ

0.03±0.02 0.06±0.04 0.12±0.04 0.16±0.05 0.11±0.07 0.07±0.04 0.02±0.01 0.03±0.02 0.05±0.04 0.08±0.04 0.16±0.06

0.03±0.02 2.88±0.15 3.15±0.14 3.96±0.17 4.02±0.18 3.27±0.18 3.11±0.18 2.26±0.12 2.08±0.16 1.78±0.18 1.62±0.18

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Therefore, CaO2 could significantly elevate the DO concentration at the

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sediment–water interface of the landscape water. Moreover, CaO2 could help maintain

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the DO concentration at a high level for a period of 50 days.

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3.1.3 Effect of CaO2 on TCOD and sulfur concentrations in the interstitial water

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ACCEPTED MANUSCRIPT Fig. 4 shows the changes in TCOD, S2−, and SO42− concentrations in the

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interstitial water of different zones. As shown in the figure, the variation trends of

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these indices were the same as those in the overlying water of different zones. The

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concentrations of TCOD and S2− in the interstitial water of CZ increased gradually

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compared to the initial value, but the concentration of SO42− decreased stably.

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However, the concentrations of TCOD, S2−, and SO42− in the interstitial water of TZ

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were contrary to those of CZ.

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Fig. 4 Time course of TCOD and sulfur in the interstitial water of different zones: (a) TCOD, −

(b) S2 and SO42

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Fig. 4(a) shows the variation trends of TCOD concentration in the interstitial

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water of different zones. As shown in the figure, the initial TCOD concentrations were

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131.74±5.28 and 136.42±6.53 mg L-1 in the interstitial water of CZ and TZ,

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respectively; the latter was slightly higher than the former. During the experiment,

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TCOD concentration increased first and reached the maximum value (198.33±7.25

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mg L-1) at the 43rd day in the interstitial water of CZ. On the contrary, the TCOD

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concentration decreased stably and reached the minimum value (86.06±5.27 mg L-1)

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at the 50th day in the interstitial water of TZ. Therefore, the average TCOD

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concentrations in the interstitial water of CZ and TZ were 163.28±5.76 and

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107.84±5.32 mg L-1 (p=0), respectively; the latter was 66.05% of the former. Fig. 4(b) shows the changes of S2− and SO42− concentrations in the interstitial

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water of both areas. The initial S2− concentrations in the interstitial water of different

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zones were the same at approximately 0.31 mg L-1. S2− concentration increased

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continually and reached the maximum value (0.92±0.13 mg L-1) at the 50th day in the

319

interstitial water of CZ, whereas the S2− concentration decreased gradually and

320

reached the minimum value (0.13±0.02 mg L-1) at the 57th day in the interstitial water

321

of TZ. During the entire experiment, the average S2− concentrations were 0.61±0.04

322

and 0.20±0.03 mg L-1 (p=0) in the interstitial water of CZ and TZ, respectively, which

323

indicated CaO2 could reduce 67.21% S2− in the interstitial water. The initial SO42−

324

concentrations in the interstitial water of CZ and TZ were similar, which were

325

20.05±2.11 and 21.18±1.73 mg L-1, respectively. SO42− concentration decreased

326

continuously in the interstitial water of CZ, whereas the concentration increased

327

stably and reached the maximum value (52.37±2.09 mg L-1) at the 50th day in the

328

interstitial water of TZ. The average SO42− concentrations were 15.51±0.98 and

329

45.27±1.62 mg L-1 (p = 0) in the interstitial water of CZ and TZ, respectively; the

330

latter was 2.92 times the former.

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In summary, CaO2 could significantly decrease the concentrations of TCOD and

332

S2− in the interstitial water but could increase the concentration of SO42−, which could

333

provide a good reference in the purification and improvement of black-odor landscape

334

water.

335

3.2 Effect of CaO2 on the sediment of landscape water 16

ACCEPTED MANUSCRIPT 336

3.2.1 Effect of CaO2 on sediment ORP Table 2 shows the variations of ORP levels in the sediment of different zones. As

338

shown in the table, the initial values of ORP level in different zones were similar, as

339

low as −342.9±15.6 and −341.8±13.5 mv in the sediments of CZ and TZ respectively.

340

During the experiment, the ORP level in the sediment of CZ decreased steadily and

341

reached the minimum value (−426.4±14.7 mv) at the 57th day. However, the ORP

342

level in the sediment of TZ increased first and reached the maximum value

343

(−160.4±13.4 mv) at the 29th day. Although the ORP levels in the sediment of TZ

344

declined later, it was still higher than that of CZ in the corresponding time. The

345

average values of ORP were −373.28±11.1 and −223.3±9.8 mv (p=0) in the sediments

346

of CZ and TZ, respectively. Therefore, CaO2 could significantly elevate the ORP level

347

in the sediment of landscape water.

348 349

Table 2 ORP levels in the sediments of different zones during the experiment

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Time（d）

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0 4 8 15 22 29 36 43 50 57 64

350 351

ORP（ （mv） ）

CZ

TZ

-342.9±15.6 -312.6±13.7 -313.7±12.8 -339.6±15.4 -378.6±14.5 -392.7±16.7 -394.2±17.8 -378.7±15.1 -410.3±16.2 -426.4±14.7 -416.8±13.7

-341.8±13.5 -317.3±14.6 -276.4±14.2 -233.2±11.3 -182.2±13.8 -160.4±13.4 -162.5±12.5 -177.8±11.7 -189.2±11.9 -200.3±12.5 -213.2±12.1

3.2.2 Effect of CaO2 on microorganisms in sediment 1) Analysis of microbial diversity

17

ACCEPTED MANUSCRIPT Table 3 shows the microbial diversity indices in the sediments of different areas.

353

The Chao and ACE indices were used to reflect the richness of the species without

354

considering the uniformity, which were positively correlated with the species. The

355

Shannon and Simpson indices were used to evaluate the species richness under the

356

premise of considering species uniformity. The Shannoneven index was used to assess

357

the uniformity of the species distribution in the samples. The Goods coverage index

358

was used to obtain the probability of the species being detected in the samples.

359 360

Table 3 Microbial diversity indices in the sediments of different areas

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Observed OTU

Chao

ACE

Control Test

1006 1129

1081 1254

1072 1221

Goods Shannoneven Coverage

M AN U

Sample

Shannon Simpson 5.916 5.853

0.9934 0.9923

0.9923 0.9919

0.8438 0.8226

As shown in Table 3, the Goods coverage indices in the sediments of different

362

zones were larger than 99%, which indicated that the sequencing depth was sufficient.

363

The values of OTU, Chao, and ACE indices in the sediment of TZ were higher than

364

those of CZ, whereas the Shannon, Simpson, and Shannoneven indices of microbial

365

species in the sediment of TZ were slightly smaller than those of CZ. Therefore, CaO2

366

could increase the diversity and abundance of microbial community in the sediment of

367

landscape water but could decrease the uniformity of microbial community structure

368

in the sediment.

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2) Analysis of microorganism community structure of phylum level

370

Fig. 5 shows the species abundances of phylum level in the sediment of different

371

zones, obtained by the RDP classifier software. Bacteria having less than 0.5%

372

abundance, together with undetermined class were uniformly named as “Others.” 18

ACCEPTED MANUSCRIPT

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Fig. 5 Relative abundances of phylum level in sediment

376

Among different species in the sediment of CZ shown in Fig. 5, Proteobacteria

377

was the dominant species (31.94%), followed by Chloroflexi (17.26%), Firmicutes

378

(10.48%), and Bacteroidetes (10.31%). Althougth the relative abundances of the

379

species varied greatly, the dominant bacteria in the sediment of TZ were similar to

380

those of CZ. Proteobacteria was still the dominant species (27.82%), followed by

381

Bacteroidetes (12.80%), Firmicutes (12.76%), and Chloroflexi (5.33%). CaO2 could

382

also affect the relative abundance of other bacteria in the sediment of TZ to a certain

383

extent. The relative abundance of Caldiserica in the sediment of TZ was 2.39%,

384

which was larger than that of CZ (1.55%). Meanwhile, the relative abundances of

385

Actinobacteria, Cyanobacteria, Spirochaetes, and Synergistetes in the sediment of TZ

386

were 1.26%, 0.63%, 1.27%, and 0.38%, respectively, which were lower than those of

387

CZ (2.38%, 1.02%, 2.33%, and 2.05%). Besides those species being found in CZ,

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ACCEPTED MANUSCRIPT 388

some unique bacteria, such as Aminicenantes (1.06%), Nitrospirae (1.22%), and

389

Thermodesulfoba (1.11%) were also detected in the sediment of TZ in phylum level.

391

Consequently, CaO2 not only could change the relative abundance of microbial species in the sediment but also could derive a certain number of new bacteria.

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3) Analysis of microorganism community structure in genera level

393

Bacteria having less than 0.3% abundance in genera level, together with

394

undetermined sequence were uniformly named as “Others.” Fig. 6 shows the species

395

abundances of genera level in the sediment of different areas.

396 397 398

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Fig. 6 Relative abundances of genera level in sediment

In this experiment, there are 243 and 258 different microbial species in genera

399

level that were detected in the sediments of CZ and TZ, respectively. The number of

400

microbial genus found in the sediments of CZ and TZ were 21 and 22, respectively, in

401

addition to the bacteria of relative abundance less than 0.3% with undetermined

402

sequence. As shown in Fig. 6, the relative abundance of microbial genus in the 20

ACCEPTED MANUSCRIPT sediments of different zones was relatively different. Among the dominant species

404

(the relative abundance higher than 2.0%) in the sediment of CZ, Petrimonas was

405

ranked first (10.83%), followed by Smithella (9.51%), Syntrophorhabdus (3.09%),

406

Proteus Hauser (2.38%), and Levilinea (2.13%). Correspondingly, Petrimonas was

407

the most dominant species (8.04%) in the sediment of TZ, followed by Smithella

408

(7.28%), Proteus Hauser (6.79%), Planctomyces (2.91%), Desulfomicrobium (2.58%),

409

and Verrucomicrobium (2.36%). Besides the same species composition in the

410

sediments of both zones, the unique bacteria of Enterobacteriaceae (1.89%), Gemella

411

(1.67%), Haemophilus (1.06%), and Streptococcus (1.95%) were detected in the

412

sediment of CZ in genera level, whereas the unique bacteria of Desulfomicrobium

413

(2.58%), Nitrobacter (1.13%), Nitrosomonas (0.52%), Syntrophomonas (1.82%), and

414

Thiobacillus (1.62%) were also found in the sediment of TZ. Meanwhile, the relative

415

abundances of specific or facultative anaerobes in genera level were decreased

416

obviously in the sediment of TZ. For example, the relative abundances of Bellilinea,

417

Caldisericum, Clostridium, Parabacteroides, and Desulfobacterium in the sediment of

418

TZ were 0.77%, 0.54%, 0.66%, 0.42%, and 0.37%, respectively, which were lower

419

than those in the sediment of CZ (1.09%, 1.39%, 1.59%, 1.58%, and 0.96%).

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In summary, CaO2 could obviously reduce the relative abundance of anaerobic

421

bacteria but maybe increase that of aerobic bacteria. CaO2 could also derive some new

422

bacteria which were well adaptive to the environment.

423

4. Discussion

424

4.1 Improving water quality by adding CaO2 to black-odor landscape water 21

ACCEPTED MANUSCRIPT CaO2, an odorless and tasteless alkaline earth metal peroxide, has long

426

persistence and good thermal stability, and is not easily affected by air humidity and

427

CO2 contents. Meanwhile, CaO2 can release oxygen slowly in water, which can

428

improve the hypoxic environment of river and lake theoretically (Chen et al., 2018).

429

According to the stoichiometric ratio, the oxygen release rate of CaO2 is as high as

430

0.222 g-O2 /g-CaO2. CaO2, as one of the common food additives, which is safe to the

431

environment and has a high industrial purity of 60%–80%. (Nelson et al., 2015).

432

Therefore, CaO2 has been widely used for oxygen generation and deodorization in

433

environmental engineering.

434

CaO2 + H2O → 0.5O2↑+ Ca(OH)2

435

CaO2 + 2H2O → H2O2 + Ca(OH)2

436

H2O2 → 2H2O + O2↑

437

CaO2 → 0.5O2↑+ CaO

(4)

438

H2O2 + activator → OH- + HO•

(5)

439

Ca(OH)2 + H2O2 → CaO2 + 2H2O

(6)

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(1) (2) (3)

Formulas (1)–(6) show the reactions between CaO2 and water. Wang et al.

441

demonstrated in their study that CaO2 was slightly soluble in water, where it

442

continued to release O2 and H2O2 in the process of dissolution, and H2O2 was further

443

reacted with active substances to produce O2• and HO• (Wang et al., 2016). Due to the

444

strong oxidizing properties of O2• and HO•, CaO2 could increase the DO

445

concentration and improve the quality of black-odor landscape water and had good

446

removal effects on other contaminants (such as: 2,4-dichlorophenol, arsenic, benzene

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ACCEPTED MANUSCRIPT 447

and heavy metals) (Qian et al., 2016; Olyaie et al., 2012; Xue et al., 2016; Chen et al.,

448

2016). The reaction of CaO2 and H2O to produce H2O2 and O2 is accompanied with the

450

formation of Ca(OH)2, which may cause a large increase in pH value of the trial water

451

theoretically. Nevertheless, the mean values of pH in CZ and TZ were 7.19±0.02 and

452

7.26±0.02 (p=0.568) for overlying water; 7.05±0.02 and 7.32±0.03 (p=0) for

453

interstitial water; 6.85±0.03 and 7.23±0.04 (p=0) for sediment (Table A in the

454

supplementary material) in our study. Thus CaO2 had no significant impact on the pH

455

value of the overlying water. Although the interstitial water and sediment in TZ was in

456

a weak-alkaline environment, the pH values were slightly higher than those of CZ.

457

This phenomenon was mainly attributed to the actual river had a strong buffer

458

capacity for the variences of pH caused by CaO2 owing to the existence of sediment

459

and the flowing and open of water area (Nykänen et al., 2012).

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In summary, CaO2 could not only improve the black-odor phenomenon of

461

landscape water but also remove other pollutants effectively from water and

462

sediments. Therefore, CaO2 is a preferred medicament for emergency treatment of

463

black-odor landscape water.

464

4.2 Mechanism of improving water quality in black-odor landscape water by CaO2

465

4.2.1 Effect of CaO2 on basic environment of landscape water and microorganisms in

466

sediment

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467

As described in Section 4.1, CaO2 could produce O2, H2O2, O2•, and HO• during

468

its dissolution procedure in water, which would effectively increase the DO 23

ACCEPTED MANUSCRIPT concentration of water and the ORP level of sediments. In our experiment, the DO

470

concentrations in the overlying water and the sediment–water interface of TZ were

471

3.78 and 32 times those of CZ, whereas the ORP levels were also significantly

472

elevated (p=0) in the overlying water and the sediments of TZ.

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CaO2 not only could improve the basic environment of the overlying water and

474

sediment but also could influence the microbial community structure of sediment to a

475

certain extent. The high-throughput sequencing results showed that the relative

476

abundances of Bacteroidetes in the sediments of CZ and TZ were 10.31% and 12.80%,

477

respectively. Bacteroidetes, as a common aerobic bacteria, could promote the

478

degradation of organic matter in sediments (Oun et al., 2017). The relative

479

abundances of Firmicutes in the sediments of CZ and TZ were 10.48% and 12.76%,

480

respectively, and its abundance was positively correlated with DO concentration but

481

negatively correlated with N content (Marra et al., 2012). The relative abundances of

482

Proteobacteria in the sediments of CZ and TZ were 31.94% and 27.81%, respectively;

483

the abundance of this common specific or facultative anaerobes in water was

484

negatively correlated with DO concentration (Lim et al., 2018). The relative

485

abundances of Chloroflexi , one of facultative anaerobes, in the sediments of CZ and

486

TZ were 17.26% and 15.33% respectively. Sorokin et al. indicated that Chloroflexi

487

lacked the functions of producing O2 and fixing nitrogen, whereas it could accelerate

488

the hydrolysis process of macromolecular substances in sediments (Sorokin et al.,

489

2012).

490

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Therefore, CaO2 could effectively improve the anoxic condition of landscape 24

ACCEPTED MANUSCRIPT water in summer, reduce the abundance of specific or facultative anaerobes, and

492

increase the relative abundance of aerobic bacteria. Moreover, a certain number of

493

functional bacteria would be generated, which were contributed to the water quality

494

purification of black-odor landscape water.

495

4.2.2 Effect of CaO2 on the concentrations of TCOD and S in water

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Our experiment exhibited that DO concentration of water and ORP level of

497

sediments in TZ were elevated effectively, which could prevent pollutants releasing

498

from sediment. Meanwhile, the TCOD concentrations in the overlying and interstitial

499

waters of TZ reduced obviously and some pollutants are removed from the landscape

500

water, which were due to the enhanced biochemical reaction and oxidation effects of

501

CaO2. The S2− concentrations in the overlying and interstitial waters were decreased

502

obviously, whereas the corresponding SO42− concentrations were increased

503

significantly. Accordingly, the water quality of black-odor landscape water could be

504

improved greatly.

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During the experiment, the mean TCOD concentrations in the overlying and

506

interstitial waters of TZ were 52.98% and 66.05% of those of CZ, which indicated

507

that the addition of CaO2 could effectively reduce the TCOD concentration of

508

landscape water. The relative abundances of Proteus Hauser in the sediments of CZ

509

and TZ were 2.38% and 6.79%, respectively, whereas those of Planctomyces were

510

0.82% and 2.91%. Chen et al. claimed that Proteus Hauser was a common microbial

511

strain in the nitrogen and phosphorus removal system, and it had a good degradation

512

ability to organic matter in sewage wastewater (Chen et al., 2010). Liu et al. indicated

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25

ACCEPTED MANUSCRIPT that Planctomyces could increase the degradation efficiency of TN, NH4+‒N, and

514

COD in leachate when they were used a two-phase anoxic/aerobic combined

515

membrane bioreactor system to dispose landfill leachate (Liu et al., 2017). Therefore,

516

CaO2 could obviously reduce the concentration of TCOD in the landscape water

517

through increasing the microbial diversity, oxidation reaction and functional bacteria

518

abundance in the sediments of TZ.

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The average S2− concentrations in the overlying and interstitial waters of TZ

520

were 29.63% and 32.79% of those of CZ throughout the test. On the contrary, the

521

corresponding values of SO42− were 2.52 and 2.92 times those of CZ, which was

522

mainly caused by the changes of microbial community structure in the sediments of

523

TZ. In the experiment, the removal rates of S2− and TCOD by adding calcium

524

peroxide were better than that of sediments directly dredging in a typical eutrophic

525

shallow lake (Liu et al., 2015). Caldisericum could reduce sulfate and thiosulfate to

526

H2S under anaerobic or anoxic conditions when it used lactic or propionic acid as an

527

electron donor in the reduction reaction (Shivaji et al., 2011). Smithella could degrade

528

alkanes and had mutual promotion effect on metabolization with methanogenic

529

archaea (Li et al., 2017). Syntrophorhabdus could produce methane, acetic acid, and

530

butyric acid through anaerobic fermentation (Li et al., 2014). In this experiment, the

531

above-mentioned genera were all detected both in the sediments of CZ and TZ.

532

However, the relative abundances of these genera in the sediment of CZ were much

533

higher than those of TZ. Meanwhile, the unique genera of specific or facultative

534

anaerobes, such as Enterobacteriaceae, Gemella, Haemophilus, and Streptococcus,

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519

26

ACCEPTED MANUSCRIPT were also detected in the sediment of CZ in genera level besides the same

536

composition of species in TZ. These genera, commonly generated during the

537

anaerobic digestion process, could promote the anaerobic fermentation process,

538

thereby increasing the concentrations of S2− in the overlying and interstitial waters of

539

CZ. The unique genera in the sediments of TZ included Desulfomicrobium,

540

Nitrobacter, Nitrosomonas, and Thiobacillus, which could enhance the removal of

541

nitrogen and sulfide in water by promoting nitrification and biodesulfurization (Gu et

542

al., 2018; Han et al., 2017). NO3− could oxidize H2S, sulfide, thiosulfate, and

543

tetrathionate to sulfate but decrease the S2− concentrations in the overlying and

544

interstitial waters of TZ when it acted as an electron acceptor in those reactions.

545

Furthermore, the products (such as O2, H2O2, HO• and O2•) from the reaction of CaO2

546

with H2O could reduce the pollutants concentrations by the oxidation effect.

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Therefore, CaO2 could significantly reduce the concentrations of TCOD and S2−

548

in the overlying and interstitial water but increase the concentrations of SO42−.

549

Accordingly, the black-odor phenomenon of landscape water could be alleviated.

550

4.2.3 Effect of CaO2 on turbidity and transparency of landscape water

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As previously described, CaO2 could effectively inhibit the process of anaerobic

552

hydrolysis, reduce the release of endogenous pollutants from sediments, and improve

553

the quality of black-odor landscape water by improving the basic environment of

554

landscape water and microbial community structure of sediment. Meanwhile, CaO2

555

could produce O2• and HO• during its dissolution procedure in the water, which had

556

strong oxidizing and bleaching properties for oxidizing Fe2+ and Mn2+ to a high

557

valence. Then, the high-valence metal ions could produce colloid with OH−, thereby 27

ACCEPTED MANUSCRIPT decolorizing in the black-odor landscape water. Moreover, CaO2 could promote the

559

function of microorganism to assimilate and degrade pollutants in water body and

560

enhance the effect of strong oxidative free radicals on decolorization and

561

deodorization. As a result, the turbidity of landscape water could be decreased,

562

whereas the transparency could be increased. The average values of turbidity in the

563

overlying water of TZ was significantly lower than those of CZ (p=0), whereas those

564

of transparency were obviously higher than those of CZ. During the entire experiment,

565

the mean value of turbidity in the overlying water of TZ was 39.46% of that of CZ,

566

whereas the mean value of transparency in the overlying water of TZ was 2.07 times

567

that of CZ. The comprehensive purification effect of black-odor water by adding

568

CaO2 was superior to using chitosan-modified clays (Huang et al., 2015).

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In summary, the addition of CaO2 could effectively inhibit the release of

570

pollutants from sediment and hinder anaerobic hydrolysis by improving the anoxic

571

condition of landscape water and the microbial community structure in sediment.

572

Simultaneously, CaO2 could obviously decrease the TCOD concentration, S2−

573

concentration, and turbidity in the overlying and interstitial waters. On the contrary,

574

CaO2 could increase the transparency and restore the ornamental value of the

575

black-odor landscape water.

576

5. Conclusions

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In the field experiment, the purification effect of CaO2 on black-odor landscape

578

water was systematically studied, and the purification mechanism was explored. The

579

main conclusions were obtained as follows:

580

1) CaO2 could effectively alleviate the black-odor phenomenon of landscape

581

water by improving the anoxic condition of water body. Meanwhile, its attributes of 28

ACCEPTED MANUSCRIPT 582

releasing oxygen slowly provides a time effect of CaO2 on the treatment of black-odor

583

landscape water, and the DO concentration in the overlying water of TZ was

584

maintained at a high level (DO > 3 mg L-1) in the entire experiment of 2 months. 2) CaO2 could increase the diversity of the microbial flora in sediments, reduce

586

the relative abundance of the specific or facultative anaerobes in sediments, and

587

derive some aerobic and functional bacteria, such as Nitrobacter, Nitrosomonas,

588

Desulfomicrobium, and Thiobacillus.

SC

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3) CaO2 could obviously reduce the concentrations of TCOD and S2− in the

590

overlying and interstitial waters of landscape water but increase those of SO42−. Thus,

591

the average concentrations of TCOD in the overlying and interstitial waters of TZ

592

were 52.98% and 66.05% of those of CZ. The average concentrations of S2− were

593

29.63% and 32.79%, which were 2.52 and 2.92 times those of SO42−. As a result, the

594

formation of odorant substances and black matters were inhibited effectively.

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4) CaO2 could effectively improve the basic environment of landscape water,

596

inhibit the release of pollutants from sediment, and promote microbial assimilation

597

and degradation rate to pollutants. Consequently, the turbidity in the overlying water

598

could be decreased, whereas the transparency could be increased.

AC C

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595

In summary, CaO2 could effectively alleviate the black-odor phenomenon and

600

excellently restore the ornamental value of landscape water. Thus, for practical

601

applications, addition of CaO2 to the black-odor landscape water has a positive effect

602

on water ecological environment and opens new avenues for the use of CaO2 in the

603

future. 29

ACCEPTED MANUSCRIPT 604 605

Acknowledgments This work was funded by the National Natural Science Foundation of China

607

(Project No. 21677115) and the Shaanxi Provincial Natural Science Foundation

608

Research Key Project (Project No. 2016JZ019).

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611

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HIGHLIGHTS： ： ·Effect of CaO2 on black-odor landscape water was firstly studied in a field test. ·CaO2 could elevate DO and ORP, thereby effectively improved the anoxic environment.

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·CaO2 could derive some functional species such as Nitrobacter and Thiobacillus. ·CaO2 reduced pollutants concentrations by enhancing biological action in sediment.

·CaO2 reduced turbidity 60.54%, TCOD 47.02% and S2− 70.37% in the overlying

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water.