Continuous in-house acidification affecting animal slurry composition

b i o s y s t e m s e n g i n e e r i n g 1 3 2 ( 2 0 1 5 ) 5 6 e6 0

Available online at www.sciencedirect.com

ScienceDirect journal homepage: www.elsevier.com/locate/issn/15375110

Research Note

Continuous in-house acidification affecting animal slurry composition Maibritt Hjorth a,*, Giorgia Cocolo b, Kristoffer Jonassen c, Lone Abildgaard a, Sven G. Sommer d a

Department of Engineering, Aarhus University, Aarhus, Denmark
Degli Studi di Milano, Milan, Italy Department of Agricultural and Environmental Sciences, Universita c Department of Housing and Environment, Danish Pig Research Centre, Copenhagen, Denmark d Institute of Chemical Engineering, Biotechnology and Environmental Engineering, University of Southern Denmark, Odense, Denmark b

article info

The emerging slurry acidification technology affects gaseous emissions, fertiliser value,

Article history:

biogas production and solideliquid separation; however, maximising the advantages is

Received 1 May 2014

difficult, as the effect of acidification on the slurry characteristics resulting in those ob-

Received in revised form

servations remains unclarified. A full-scale study was therefore performed, comparing pig

3 February 2015

slurry from normal in-house slurry management with pig slurry from housing with daily

Accepted 16 February 2015

in-house acidification to pH 5.5. The effect on organic, inorganic and particles was evalu-

Published online 4 March 2015

ated. Increasing dissolved P, Mg and Ca contents indicated mineral dissolution in acidified slurry. Acceleration of carbohydrate hydrolysis was indicated, while deceleration of mi-

Keywords:

crobial acidogenesis, acetogenesis, methanogenesis and sulphate reduction was indicated.

Manure

The particles were larger following acidification treatment causing a lower viscosity, likely

pH reduction

due to acidification-induced aggregation. Overall, the acidified slurry was significantly

Organic degradation

different from untreated slurry; it had higher conductivity, more dissolved inorganic

Inorganic dissolution

components, fewer small organic compounds, more large dissolved organic compounds,

Particle aggregation

and larger particles. © 2015 IAgrE. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

Animal slurry acidification minimises the societal problematic NH3 emission (Kai, Pedersen, Jensen, Hansen, & Sommer, 2008; Wang, Huang, Ying, & Luo, 2014). National legislation therefore favours this technology (Danish Ministry of Environment, 2013). In Denmark below 2% of the slurry was acidified in 2008, while 10% was acidified in 2012 (Birkmose &

Vestergaard, 2013). One solution is continuous in-house acidification, installable in new and existing housings. The pH targeted differs between available technologies (5.5e6.4), but depend on the intended NH3 emission reduction and treatment duration. Lower emissions of CH4 (Ottosen et al., 2009; Petersen, Andersen, & Eriksen, 2012; Wang et al. 2014) and, in some studies, H2S (Eriksen, Andersen, Poulsen, Adamsen, &

* Corresponding author. Hangøvej 2, 8200 Aarhus N, Denmark. Tel.: þ45 4082 5988. E-mail address: [email protected] (M. Hjorth). http://dx.doi.org/10.1016/j.biosystemseng.2015.02.009 1537-5110/© 2015 IAgrE. Published by Elsevier Ltd. All rights reserved.

b i o s y s t e m s e n g i n e e r i n g 1 3 2 ( 2 0 1 5 ) 5 6 e6 0

Petersen, 2012) has been observed from stored acidified slurry than from untreated slurry. Increased plant growth has been observed upon fertilisation with acidified slurry (Petersen, Lemming, & Rubæk, 2013). Biogas production from acidified slurry has been observed to be lowered (Moset, Cerisuelo, Sutaryo, & Moller, 2012) and the solid products of solideliquid separation have been observed to contain less nutrients (Fangueiro, Ribeiro, Vasconcelos, Coutinho, & Cabral, 2009). Hence, the slurry characteristics must be changed by the acidification. Precipitation and dissolution of inorganic minerals are pH controlled. Anaerobic degradation is mediated by microorganisms and enzymes, which are sensitive to the media conditions including pH and conductivity. Particle sizes depend on the pH controlled slurry composition. The dominant reactions in complex chemical and biological mixture as animal slurry cannot be calculated, and the resulting slurry composition must therefore be assessed experimentally. This study aimed to quantify the effect of in-house continuous acidification on the organic turnover, mineral dissolution and particle sizes under full-scale conditions. This was done by analysing the physical, organic, inorganic and emission characteristics of untreated slurry and in-house acidified slurry.

2.

Materials and methods

Slurry was collected from two identical experimental sections, each housing 64 finishing pigs. The slurry in one section was acidified daily with H2SO4, while in the other section, the slurry was left untreated. The pig house was managed using Danish standard guidelines.

2.1.

Slurry treatment

Slurry channels with non-acidified slurry were emptied to a storage container only twice during the period. The equipment for acidifying slurry consisted of one external 14 m3 treatment tank, to which 96% H2SO4 was added automatically until pH 5.5 (Infarm A/S, Aalborg). Slurry from the channels was flushed to the tank daily, and acid added. The duration of filling, treating and emptying was 1.5 min, 5e10 min and 2.5 min. Eight cubic meter acidified slurry was returned to the channel, and surplus slurry, approximately 5% by volume, was transferred to a storage container. Cleaning water was avoided. Treatment (A) ran for 77 days from February 2012, and the pigs grew from 31 to 108 kg. In each section, 21 m3 slurry was produced and a total of 8.4 L H2SO4 m3 was added. A secondary treatment (B) ran under equivalent conditions for 70 days from September 2012, and the pigs grew from 33 to 104 kg. In each section, 21 m3 slurry was produced, and a total of 9.5 L H2SO4 m3 was added to retain pH 5.5. By the end of each period, subsamples were collected from the storage container. Samples were stored a maximum of 3 days at 5C for physical analyses or at 18C for chemical analysis.

2.2.

57

Physical and chemical analyses

Total sulphur, phosphorus, magnesium and calcium were determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The dissolved amounts were determined by ICP-OES in supernatant after 14,000 rpm-centrifugation. Dry matter (DM) and volatile solid were determined according to APHA (2005). Hemicellulose, cellulose and lignin € gana € s, Swewere determined using a Fibertec 2010 (Foss, Ho den) (Van Soest, 1963). Free reduced carbohydrate content was measured at 540 nm in supernatant after dinitrosalicylic acidderivatisation (Miller, 1959) using glucose standards. Total Kjeldahl nitrogen (N tot) and total ammoniacal nitrogen (TAN) were determined using a Kjeltec 2011 instrument (Foss, € gana € s, Sweden) (APHA, 2005). Volatile fatty acids were Ho measured according to Moset et al. (2012). Total inorganic carbon (TIC) was determined by adding HCl, re-collecting the emitted CO2 in NaOH, and titrating with HCl. Sulphide was quantified according to Eriksen et al. (2012). The pH and conductivity were measured using standard electrodes. Particle size distribution and zeta potential were measured with a Master sizer 2000 (Malvern Instruments Ltd, Worcestershire, UK), using tap water or 0.2 M KCl for dilution, respectively, after 1 mm sieving. Viscosity was measured using a Viscometer and a LV-1 spindle at 50 rpm (Brookfield, MA, USA); particle size distribution and viscosity were performed a rapidly as possible. Atmospheric NH3 in ventilation air from housing sections was measured during the full period with an infrared analyser (INNOVA 1412 and INNOVA 1309, LumaSense, Ballerup, Denmark). In the laboratory, 200 ml slurry samples were stored for 35 days in N2 flushed sealed 500 ml bottles. Gas volumes were measured by water displacement. The contents of H2S, CH4 and CO2 in the gas were determined according to Moset et al. (2012). Measurements of slurry dry matter, volatile solids, volatile fatty acids and particle sizes were performed to check for comparability between the two experimental periods A and B, and the periods proved comparable. All analyses were performed in triplicate, except Mg, Ca, S tot, fibre analysis and TIC that were each performed in duplicate. With exception of soluble Mg, the coefficients of variance of the duplicate analysis were below 8% (Table 1).

2.3.

Data analysis

The significance of the conversions was evaluated by balancing C, N, S, P, Mg and Ca (labelled X) amounts:
Creaction ¼ m Xproduct *mðXreactant Þ1

(1)

with product and reactant depending on the reaction, and m being mass expressed in g kg1 DM.

3.

Results

Addition of H2SO4 reduced pH in slurry, and increased tot-S in the slurry (Table 1). The NH3 concentration in housing air was reduced by 70%, hence comparable with previous studies (Kai et al., 2008). The required H2SO4 addition varied by 11%

58

b i o s y s t e m s e n g i n e e r i n g 1 3 2 ( 2 0 1 5 ) 5 6 e6 0

Table 1 e Chemical and physical characteristics of untreated slurry and continuous in-house acidified slurry. Numbers in parentheses are standard deviations. Control slurry pH NH3(g)a, housing S tot Dry matter P(aq)b P(s)c Mg(aq) Mg(s) Ca(aq) Ca(s) Volatile solids Lignin Cellulose Hemicellulose Free carbohydrates Protein þ amino acidsd Pentanoic acid Methylbuturic acid þ isovaleric acid Butanoic acid Iso-butanoic acid Propionic acid Acetic acid TIC H2S tot TAN CH4(g), storagee CO2(g), storage H2S(g), storage Conductivity Zeta potential Viscositye Particles 0.01e1 mm Particles 1e100 mm Particles 100e1000 mm a b c d e f g

ml L1 g kg1 DM g kg g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM g kg1 DM mS cm1 mV mPa s vol %g vol % vol %

7.11 21 6.4 91 1.4 16 0.3 8.9 5.7 20 780 79 170 170 13 200 4.6 13 31 10 40 110 90 0.046 60 6.7 35 0.39 26.6 14 66 0.8 61 38

(0.03) (1) (0.0) (0) (0.0) (3) (0,0) (1.6) (0.0) (2) (10) (7) (0) (4) (1) (0) (0.1) (0) (1) (0) (0.01) (3) (10) (0.002) (0) (0.1) (0) (0.01) (0.6) (2) (1) (0.1) (5) (4)

Acidified slurry 5.33 5.6 53 83 11 1.6 7.5 0.0 16 4.3 760 71 93 120 30 220 8.3 5.6 42 3.0 28 66 10 0.0045 49 0.46 12 0.023 28.0 9.6 25 0.3 45 54

(0.01) (0.5) (1) (1) (1) (0.8) (0.2) (0.0) (1) (0) (11) (5) (4) (7) (1) (0) (0.0) (0.0) (0) (0.0) (0) (0) (5) (0.0001) (0) (0.09) (0) (0.000) (0.4) (0.7) (1) (0.0) (1) (0)

Statistical changef e e þ e þ þ þ e e e þ þ þ e þ e e e e e e e e e þ Ie I e þ þ þ

(g) ¼ gas state. (aq) ¼ dissolved state. (s) ¼ solid state. Calculated as (N tot e TAN)/16.5%. Results from acidification treatment B-samples instead of A-samples. No symbol: no statistical difference (P > 0.05), : decreasing, þ: increasing, I e I: numeric decreasing. Volume % of 0.01e1000 mm diameter particles.

between period A and B, likely linked to the growth period lengths, minor variations in slurry content, and farm management. Thus, the acidification treatments ran as planned. The conductivity was increased. And the dissolved levels of phosphorus, magnesium and calcium were all larger in acidified slurry compared to non-acidified slurry (Table 2). The cellulose and hemicellulose level was lowest in the acidified slurry, and free carbohydrate level highest in the acidified slurry. Thus, a relatively larger content of carbohydrate hydrolysis products was observed (Table 2). The levels of free carbohydrates and the sum proteins and amino acids were larger in the acidified slurry. The level of larger volatile acids (4 and 5 carbons) was equal in the two slurries, while the level of acetic acid and ammonia were lower in the acidified slurry. Thus the content of acidogenesis products (large volatile fatty acids, acetic acid and ammonia) was observed to be lower relative to the input components to the acidogenesis.

The level of the larger acids was observed to be similar between the two slurries. The acetic acid, carbonate and emitted carbon dioxide were observed to be lower in/from the acidified slurry. Thus, the acetogenesis products (acetic acid, carbonate and CO2) were observed to be present in lower amounts relative to the input components (large acids) to the acetogenesis. The level of acetic acid in the slurry, and the CO2 and CH4 emitted during a subsequent storage were all lower in/from the acidified slurry. The CO2 and CH4 emissions were decreased more than acetic acid concentrations. Thus, less product from the methanogenesis (CH4 and CO2) relative to the inputs components were present in the acidified slurry. The total sulphur level was higher in the acidified slurry, mainly due to the addition of H2SO4 as acidifying agent. The dissolved sulphide content and emission during the subsequent storage were lower from the acidified slurry. Thus, a

59

b i o s y s t e m s e n g i n e e r i n g 1 3 2 ( 2 0 1 5 ) 5 6 e6 0

Table 2 e Level of microbial and chemical conversions in slurries, see Eq. (1). A ratio >1 indicates dominance of C, N, S, P, Mg or Ca in product. Conversion likely dominated in the slurry with highest ratio. Numbers in parentheses are standard deviations. Ratio of products: reactantsa

Control

Slurry

Acidified

Slurry

m(P(aq)): m(P(s)) m(Mg(aq)): m(Mg(s)) m(Ca(aq)): m(Ca(s)) m(Cfree carbohydrate): m(Ccellulose þ hemicellulose) m(Cacetic acid): m(Cfree carbohydrate) m(NTAN): m(Namino acid þ protein) m(Cacetic acid): m(Cc4-5 acids)b m(CCH4(g)): m(Cacetic acid) m(CCO2(g)): m(Cacetic acid) m(SH2S(aq)): m(SnonH2SeS(aq))c

0.09 0.03 0.29 0.04 3.2 1.3 0.50 0.31 0.58 0.0068

(0.02) (0.01) (0.03) (0.00) (0.3) (0.0) (0.00) (0.01) (0.01) (0.0002)

6.9 >10 3.6 0.13 0.96 0.99 0.34 0.03 0.28 0.0001

(0.05) (- - -) (0.2) (0.00) (0.02) (0.00) (0.00) (0.01) (0.00) (0.0000)

Conversion Mineral dissolution

Hydrolysis Acidogenesis Acetogenesis Methanogenesis Sulfate reduction a b c

Masses (in g kg1 DM) of C, N, S, P, Mg or Ca in individual compounds, based on Table 1. c4-5 acids equal the sum of pentanoic-, methylbutyric-, isovaleric-, iso-butanoic- and butanoic acid. NonH2SeS equals the S amount of H2S(aq) subtracted from the total S.

lower relative content of microbial sulphate reduction products (sulphide and gaseous H2S) were present. The particles were larger in the acidified slurry compared with non-acidified slurry (Table 1). This was supported by a lower viscosity. Measured as the immobile charge on the particle surface, i.e. the zeta potential, the surface-attached groups were in the acidified slurry less negative.

4.

Discussion

4.1.

Mineral dissolution

The observed larger concentration of soluble phosphorus, magnesium and calcium in the continuously in-house acidified slurry compared to slurry from normal operation indicates that minerals were dissolved at pH 5.5 (Table 2). The increased conductivity observed, supported the solubilisation of the majority of inorganic precipitates upon acidification. Fangueiro et al. (2009) did in agreement observe larger soluble concentrations after acidification. Previous studies has shown struvite (MgPO4NH4  6H2O) and dicalcium phosphate (CaHPO4) to be abundant in animal slurry (Gungor, Jurgensen, & Karthikeyan, 2007). These could be the minerals dissolved upon acidification.

4.2.

Organic turnover

The initial degradation step of carbohydrates e hydrolysis e from cellulose and hemicellulose to sugar was indicated to increase in acidified slurry, based on the observed larger carbohydrate hydrolysis product amount (Table 2). Hydrolysis is typically catalysed by exoenzymes. The hydrolysis may in the acidified slurry be chemically induced. Addition of H2SO4 and heating to 100e200  C for up to 60 min is a typical method to perform chemical hydrolysis (Kumar, Barrett, Delwiche, & Stroeve, 2009). In this study, the temperature was only 20  C, but the treatment time was much longer. An increased chemical hydrolysis is therefore likely. The microbial acidogenesis, acetogenesis and methanogenesis was indicated to be inhibited by the acidification,

based on the observed lower content of acidogenesis, acetogenesis and methanogenesis products relative to the reaction inputs (Table 2). This would explain the results of previous studies; increased content of butyric acid, lowered oxygen consumption and lowered methane production has been observed in acidified slurry compared to control slurry (Ottosen et al., 2009; Petersen et al. 2012; Sorensen & Eriksen, 2009; Wang et al., 2014). Changes in slurry characteristics from excretion to acidification included a lower pH, higher conductivity, and higher content of free metals. Despite two months of storage in the slurry channels, the microbial community did not appear adapt well to the new conditions. Lowered microbial sulphate reduction was indicated in the acidified slurry, based on the observed lower relative content of sulphate reduction products. Sulphide emission has previously been observed high when H2SO4 acidified slurry was added to slurry at pH above 7 (Moset et al., 2012). Thus, the low pH in the acidified slurry may be the cause of lower activity of the sulphate-reducing bacteria.

4.3.

Particle sizes

The observed particle size increase in the acidified slurry could be due to particle aggregation of minor organic and inorganic compounds. The observed higher ionic strength and increased amount of dissolved divalent ions will, according to the DLVO theory (Gregory, 1989), cause the electrostatic layer around the particles to become thinner. The consequence of this, together with the observed lower surface charge, may be less repulsion between the particles. And acidification could therefore cause coagulation and particle agglomeration.

4.4.

Animal slurry utilisation impacts

Because lowering of pH induced a changed slurry composition, the subsequent slurry application could be affected. The fertiliser value may increase due to the lowered ammonia emission, and the increased inorganic dissolution. Phosphorus crystallisation and re-cycling may be simplified by the phosphorus dissolution. The energy production value may be enhanced by the higher content of large dissolved organic

60

b i o s y s t e m s e n g i n e e r i n g 1 3 2 ( 2 0 1 5 ) 5 6 e6 0

components, but lowered by the initially lower pH, larger S content and larger availability of potential metal inhibitors in biogas production. The particle sizes changed; hence also solideliquid separation techniques can be affected. The odour can change because of protonation of potential emitting compounds, and decreased degradation of dissolved organic compounds. And lastly because of the observed reduced methanogenesis, greenhouse gas emissions may be lowered.

Acknowledgement The authors wish to acknowledge the grant from the Danish Council for Strategic Research 09-067246. The authors wish to thank the company Infarm A/S for performing the acidification treatments.

references

APHA. (2005). Standard methods for the examination of water and wastewater. Washington, DC: American Public Health Association. Birkmose, T., & Vestergaard, A. (2013). Acidification of slurry in barns, stores and during application: review of Danish research, trials and experience. In Proceedings from Ramiran 2013. Versaille: France. Danish Ministry of Environment. (2013). Order on commercial livestock, livestock manure, silage etc. Copenhagen: Danish Ministry of Environment. Eriksen, J., Andersen, A. J., Poulsen, H. V., Adamsen, A. P. S., & Petersen, S. O. (2012). Sulfur turnover and emissions during storage of cattle slurry: effects of acidification and sulfur addition. Journal of Environmental Quality, 41, 1633e1641. Fangueiro, D., Ribeiro, H., Vasconcelos, E., Coutinho, J., & Cabral, F. (2009). Treatment by acidification followed by solidliquid separation affects slurry and slurry fractions composition and their potential of N mineralization. Bioresource Technology, 100, 4914e4917.

Gregory, J. (1989). Fundamentals of flocculation. Critical Reviews in Environmental Control, 19, 185e230. Gungor, K., Jurgensen, A., & Karthikeyan, K. G. (2007). Determination of phosphorus speciation in dairy manure using XRD and XANES Spectroscopy. Journal of Environmental Quality, 36, 1856e1863. Kai, P., Pedersen, P., Jensen, J. E., Hansen, M. N., & Sommer, S. G. (2008). A whole-farm assessment of the efficacy of slurry acidification in reducing ammonia emissions. European Journal of Agronomy, 28, 148e154. Kumar, P., Barrett, D. M., Delwiche, M. J., & Stroeve, P. (2009). Methods for pretreatment of lignocellulosic biomass for efficient hydrolysis and biofuel production. Industrial & Engineering Chemistry Research, 48, 3713e3729. Miller, G. L. (1959). Use of dinitrosalicylic acid reagent for determination of reducing sugar. Analytical Chemistry, 31, 426e428. Moset, V., Cerisuelo, A., Sutaryo, S., & Moller, H. B. (2012). Process performance of anaerobic co-digestion of raw and acidified pig slurry. Water Research, 46, 5019e5027. Ottosen, L. D. M., Poulsen, H. V., Nielsen, D. A., Finster, K., Nielsen, L. P., & Revsbech, N. P. (2009). Observations on microbial activity in acidified pig slurry. Biosystems Engineering, 102, 291e297. Petersen, S. O., Andersen, A. J., & Eriksen, J. (2012). Effects of cattle slurry acidification on ammonia and methane evolution during storage. Journal of Environmental Quality, 41, 88e94. Petersen, J., Lemming, C., & Rubæk, G. H. (2013). Side-band injection of acidified cattle slurry as starter P-fertilization for maize seedlings. In Proceedings from Ramiran 2013. Versailles: France. Sorensen, P., & Eriksen, J. (2009). Effects of slurry acidification with sulphuric acid combined with aeration on the turnover and plant availability of nitrogen. Agriculture Ecosystems & Environment, 131, 240e246. Van Soest, P. J. (1963). Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. Journal of Official Agricultural Chemists, 46, 829e835. Wang, K., Huang, D., Ying, H., & Luo, H. (2014). Effects of acidification during storage on emissions of methane, ammonia, and hydrogen sulfide from digested pig slurry. Biosystems Engineering, 122, 23e30.