- Email: [email protected]
Treatment of a low-strength bilge water of Caspian Sea ships by HUASB technique
Ecological Engineering 82 (2015) 272–275
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Short communication
Treatment of a low-strength bilge water of Caspian Sea ships by HUASB technique Seyyed Mohammad Emadian a , Morteza Hosseini b , Mostafa Rahimnejad c,d, * , Mohammad Hassan Shahavi b , Behnam Khoshandam a a
Department of Chemical Engineering, Semnan University, Semnan, Iran Department of Chemical Engineering, Babol University of Technology, Babol, Iran Biofuel & Renewable Energy Research Center, Faculty of Chemical Engineering, Babol Noshirvani University of Technology, Babol, Iran d Advanced Membrane & Biotechnology Research Center, Faculty of Chemical Engineering, Babol Noshirvani University of Technology, Babol, Iran b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 July 2014 Received in revised form 16 January 2015 Accepted 5 April 2015 Available online xxx
Oily bilge water is one of the major pollutants that threats marine environment due to its direct discharge from ships into sea. The aim of this paper is to investigate the possibility of dilute bilge water treatment by using hybrid up-flow anaerobic sludge blanket (HUASB) bio-reactor. The reactor operated at two hydraulic retention times (HRTs) of 10 h and 8 h. The organic loading rate (OLR) was gradually increased from 0.12 g to 0.6 g chemical oxygen demand (COD)/l day. After the immobilization of sludge on the surface of the support materials and 10 days of batch feeding of the reactor with the waste water as acclimation period (with COD removal of 59%), the continuous operation of the reactor started. At the end of the experiment, with the HRT of 8 h and OLR of 0.6 g COD/l day, the COD removal efficiency reached the amount of 75%. Furthermore, the bio-reactor showed a good performance in removing oil from the waste stream which was significantly lower than the standard value which has been laid down for the discharge of the bilge water from ships by the International Maritime Organization (IMO). The obtained data demonstrated that the HUASB reactor is an appropriate system for the treatment of a low-strength bilge water. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Anaerobic treatment HUASB reactor COD pH Oil content
1. Introduction Bilge water is a corrosive mixture of seawater containing a variety of constituents including cleaning agents, solvents, fuel, lubricating oils and hydraulic oils. The International Maritime Organization (IMO) regulates the discharge limit for ships which is 15 mg/l (MARPOL, 1973). Oil water separators (OWS) are usually employed to treat bilge water. OWS processes are gravity separators based on the density variation between oil and water phases. Cleaning agents in bilge water can create an emulsion of oil in water. When the emulsification takes place, buoyancy difference of oil and water is too small to be treated properly via the existing OWS technology. In recent years, several researches are conducted on bilge water treatment methods including ultrafiltration (UF), electrocoagulation and UF/photocatalytic oxidation. Peng et al. (2005) stated that
* Corresponding author. Tel.: +98 1113234204. E-mail addresses: [email protected], [email protected] (M. Rahimnejad). http://dx.doi.org/10.1016/j.ecoleng.2015.04.055 0925-8574/ ã 2015 Elsevier B.V. All rights reserved.
the microfiltration of bilge water as a pretreatment stage is desirable because used oils and particulates can block the feed channels of UF spiral. However, some reports indicated the disadvantages which associated with the application of membrane in treatment of bilge water. These disadvantages contain their relatively high cost of production due to the expensive raw materials, fouling which has a number of negative effects such as the reduction in membrane flux, additional capital and maintenance cost because of membrane replacement and regeneration. Karakulski et al. (1998) used a laboratory-scale ultrafiltration pilot plant with tubular membranes for the treatment of bilge water. However, the use of additional photo catalytic oxidation stage was necessary to eliminate the residual oil. Rincon and La Motta, (2014) investigated the treatment of synthetic ship bilge water in an electrocoagulation system. They concluded that the electrocoagulation process was an effective method in destabilizing of oil in water emulsions and removing the heavy metals. However, the authors applied additional flotation method to improve the treatment performance. Sun et al. (2010) investigated on the performance of biofilm-membrane bio-reactor (MBR) for treating bilge water. Although the efficiency of the reactor in removal of
S.M. Emadian et al. / Ecological Engineering 82 (2015) 272–275
COD and oil was promising, the membrane was seriously fouled without a recycling side-stream to the bio-reactor. In this study, anaerobic treatment has been chosen because it is an efficient, simple and economical method. It is also environmentally-friendly way. The hybrid up-flow anaerobic sludge blanket (HUASB) reactor configuration has combined both suspended and fixed growth of bacteria in one reactor. It has also used the advantages of both up-flow anaerobic sludge blanket (UASB) and up-flow anaerobic fixed film (UAFF) reactors. This kind of reactor is efficient in the treatment of dilute to high strength wastewaters at low to high organic loading rates. Bilge water is classified in the low-strength group of wastewater. Although anaerobic process is used for the treatment of medium and high strength wastewaters, it has already been applied successfully for a number of waste streams including low-strength wastewaters. Also, the efficiency of HUASB reactor (on the basis of COD and oil removal) in treatment of low-strength bilge water under different low organic loading rates has been studied.
273
the sample surface. The sample surface was also collected in a closed bottle. 2.4. Analytical methods Several monitoring parameters were evaluated during the entire operation, including COD and oil concentrations, as well as pH and temperature. For COD analysis, HACH’s Method 8000, a combination of reactor digestion method and colorimetric method, was used (DR/890, 2009). This method is equivalent to standard method 5220D: closed reflux, colorimetric method (APHA, 2008). Analysis of oil was determined according to USEPA 1664 and n-hexane gravimetric methods. Temperature and pH were measured by using a pH/temperature probe (HANNA, PH212, Germany) with automatic temperature compensation. The method used in pH measurement was generally in compliance with Standard Method 4500B (APHA, 2008). 2.5. Start-up and operation scheme
2. Material and methods
2.2. Wastewater characteristics The bilge water was collected from the ships which had anchored at Amirabad port, Behshahr, Mazandaran, Iran. The HUASB reactor was fed with bilge water pre-settled for 10 min. The characteristics of pre-settled bilge water were as follows: pH: 8–9, COD: 20–200 mg/l, total solid (TS): (800–2400) mg/l, TSS: 220–1760 mg/l, total nitrogen: 836 mg/l and total phosphorus (TP): 211 mg/l (TN and TP were measured in COD = 50 mg/l). The pH of the feed was adjusted to 6.8–7.2 by adding diluted HCl. The only supplementary nutrient, MgNO3, was added to yield a COD (N ratio of 250:5) as a nitrogen supply.
250
start-up-
later opration
0.9
200
0.75 0.6
150
0.45
100
2.3. Inoculum (seed sludge)
0.3 50
The reactor was seeded with a mixture of activated sludge from the aerobic wastewater treatment of the Mazandaran pulp, paper industry and a non-granular sludge obtained from a UASB reactor operating with cheese whey wastewater from the Gela food industry of Amol, Mazandaran, Iran. The TSS of the mixture was 13 g/l. The non-granular sludge was methanogenically active as the biogas bubbles which were apparently observed from stripping of
0.15
0
0 1
21
41
61 81 101 121 Operation time (day)
Influent COD
HRT
141 OLR
Fig. 1. Start-up and operation scheme for UASFF reactor.
OLR (g COD/l day)
The fabricated Plexiglass reactor column with an internal diameter of 4.4 cm and a liquid height of 194 cm was used. The column included three sections: bottom, middle and top sections. The bottom part of the column, with a volume of 1823 ml operated as a UASB reactor whereas the middle part of the column with a volume of 855 ml was used as a fixed film reactor. The top part of the bio-reactor with a volume of 273 ml was an unpacked column prior to the effluent overflow. The fixed film section of the column was randomly packed with 270 billowy pieces of PVC rings which had a diameter of 15 mm. The height of each ring was equal to 13 mm (150 m2/m3 specific surface areas for each one). The media in the reactor were stabled by using a plastic mesh. The wastewater as a substrate was continuously fed to the base of the reactor which was located under the bed of active sludge and through a T-inlet connected to a peristaltic pump. An outlet was provided at the top of the reactor that was connected to a 1 l funnel shaped settling compartment served as a sedimentation part where the final effluent was collected from the top of this tank. The reactor operated at ambient temperature (15–25 C).
Start-up period is usually a time consuming period. In order to decrease the time, the immobilization of biomass on the support material was done; therefore, the mentioned mixture of sludge was used by means of a technique described by Zaiat et al. (1994). The support material together with the sludge was stored in 1.5 l closed bottle and homogenized for the period of a week so as to secure steadier immobilization of bio-particles in the supporting material. After this stage, the packing material filled in its place in the HUASB reactor. The reactor was inoculated with 500 ml of the same sludge mixture. In order to acclimatize the sludge with bilge water, the daily batch feed reactor with the bilge water (50 mg/l) was selected for 10 days. After each feed, the liquid content of the reactor was continuously circulated for 1 day (until the next feed). The acclimation period permitted oxygen level to decrease to prevent inhibition of anaerobic bacteria as well as the bacteria population to adjust with the feed wastewater. The TSS concentration of the sludge after the 10-day batch-fed period was 16.5 g/l. A COD removal efficiency of about 59% was achieved at the end of this acclimation period. The start-up was carried out by using stepped organic loading to produce the most rapid biomass development. The HRT of 10 h was kept constant throughout the start-up duration and the OLR increased from 0.12 g to 0.24 g COD/l day. The reactor was allowed to reach steady state condition before each OLR change. When effluent COD reached a relatively constant value, the steady state condition was achieved and then influent OLR can be raised. The experimental procedure has been illustrated in Fig. 1.
Influent COD (mg/l) HRT (h)
2.1. Experimental apparatus
274
3. Results and discussion 3.1. Bio-reactor performance 3.1.1. pH Changes in acidity (pH) of the effluent from the HUASB reactor during the operation has been shown in Fig. 2. As it is shown in Fig. 2, the pH was comparatively stable (varying from 8.04 to 8.78) during the operation, which was suitable for efficient methanogenesis. This indicated that the system had sufficient alkalinity to neutralize organic acids coming from the hydrolysis and fermentation stage. One can see in Fig. 2 that there are numbers of decrease in pH through the operation attributed to the accumulation of the produced volatile fatty acid (VFA) due to enhancement of the influent OLR. Accumulation of VFA in the reactor did not sour the reactor. The similar result was reported by Van Haandel and Lettinga (1994) which was about the treatment of domestic wastewater. There was a sudden decrease in pH from 8.52 at day of 96 to 8.1 at day of 111 because the effect of the nutrient was tested at this stage of the operation. For testing this effect, from day of 96 to day of 101, the addition of the nutrient was ceased and after that the new nutrient, NH4Cl, was added to the reactor till day of 111. In this period of the operation, decrease in pH connected to the lower activity of the methanogenic bacteria which is responsible for consuming of the VFA. However, the reactor recovered itself because of reintroducing of MgNO3 as the nutrient to the reactor and pH increased again which is indicative of the increment in methanogenic bacteria activity. 3.2. COD removal efficiency The bio-reactor performance during the operation is shown in Fig. 3. The reactor was fed with an influent COD of 50 mg/l and 100 mg/l during the start-up stage. As it is shown in Fig. 3, the COD removal efficiency increased from 40% at the beginning of the start-up to 75% at the end of the operation implying that the sludge was acclimated appropriately to the bilge water. Each increment in OLR during the operation led to a reduction in COD removal efficiency. A comparison between Figs. 2 and 3 shows a similar trend between effluent pH and COD removal efficiency which concurs with results obtained by Zhang et al. (2008). The sudden
Effluent pH
0.8
start-up
9.3
later operation
9.1
0.7 0.6
8.9 8.7
0.5
8.5
0.4
8.3
0.3
8.1
100 80 60 40 20 0 1
21
41
61
81
101
121
141
Operating time (day) Influent COD
Effluent COD
COD Removal
Fig. 3. Bioreactor performance during operation.
decrease is attributed to the more VFA production due to the introduction of new OLR to the reactor. Similar observation was reported by other authors. The system recovered shortly and adapted to the new condition with time. Additionally, it is clearly understood that the initial immobilization of microorganisms on the surface of the support materials had a key role in shortening the start-up procedure. As it was mentioned before, the effect of the nutrient on the performance of the reactor was tested during the days of 96–111. According to Fig. 3, the COD removal efficiency decreased from 77% to 42% during the days of 96–101. In this period, adding MgNO3 to the reactor was ceased. After that, by addition of new nutrient (NH4Cl) to the reactor, the COD removal efficiency showed a little increase and reached an amount of 50% at the day of 111. Therefore, MgNO3 was reintroduced to the reactor from day of 111. By increasing the COD influent and reintroducing MgNO3 as the nutrient to the reactor, the COD removal efficiency raised again and it reached an amount of the 75% at the end of the study which was much higher than the result was obtained by Sun et al. (2010). They reported that the COD removal efficiency of moving biofilm bioreactor (an aerobic bio-reactor) in treating shipboard wastewater (including synthetic bilge water) was about 59% in HRT of 8 h. For improving the performance of the bio-reactor, they applied a membrane as a post treatment stage with a recycle-stream to the bio-reactor (Sun et al., 2010). The TSS concentration of the sludge in the reactor increased from 16.5 g/l at the beginning of the start-up to 67 g/l at the end of the study so that the sludge acted as a filter for removing the suspended solids from the wastewater. Subsequently, the UASB reactor had a noticeable effect on removing the TSS content of the wastewater.
OLR (g COD/l.day)
9.5
120
later operation
start-up
220 200 180 160 140 120 100 80 60 40 20 0
0.2
7.9
0.1
7.7 7.5
0 1
21
41 61 81 101 121 141 Operating time (day) pH
OLR
Fig. 2. Change of pH during operation.
COD removal efficiency (%)
During the experiment, COD reduction and pH were monitored daily. Also, oil reduction was checked 2 times throughout the experiment, firstly after the end of the start-up period. The second check was also after the completion of the whole experiment.
Influent and Effluent COD (mg/l)
S.M. Emadian et al. / Ecological Engineering 82 (2015) 272–275
Fig. 4. Oil removal at two point of operation.
S.M. Emadian et al. / Ecological Engineering 82 (2015) 272–275
275
3.3. Oil content
References
The reduction of oil content for the wastewater at the end of start-up and operation of the reactor has been shown in Fig. 4. It can be seen in Fig. 4 that either at the end of the start-up or the operation, the oil effluent concentration was below 15 mg/l which is a standard level for discharging the wastewater from ships (MARPOL, 1973). Sun et al. (2010) obtained that the residual oil concentration of about 30 mg/l from the effluent of the MBBR reactor in HRT of 8 h which was double times higher than the standard level (15 mg/l).
APHA, 2008. Standard Methods for the examination of Water and Wastewater. American Public Health Association/American Water Work Association/Water Environmental Federation, Washington, DC. DR/890, 2009. colorimeter, Procedures Manual, Method 8000. in: Hach Company L., CO, ed. Karakulski, K., Morawski, W.A., Grzechulska, J., 1998. Purification of bilge water by hybrid ultrafiltration and photocatalytic processes. Sep. Purif. Technol. 14, 163–173. MARPOL, 1973. International Convention for the Prevention of Pollution from Ships, 1973, as modified by the protocol of 1978 relating thereto (MARPOL 73/78). in: (IMO) I.M.O., ed. Peng, H., Tremblay, A.Y., Veinot, D.E., 2005. The use of backflushed coalescing microfilteration as pretreatment for the ultrafilteration of bilge water. Desalination 181, 109–120. Rincon, G.J., La Motta, E.J., 2014. Simultaneous removal of oil and grease, and heavy metals from artificial bilge water using electrocoagulation/flotation. J. Environ. Manage. 144, 42–50. Sun, C., Leiknes, T., Weitzenbock, J., Thorstensen, B., 2010. Development of an integrated shipboard wastewater treatment system using biofilm-MBR. Sep. Purif. Technol. 75, 22–31. Van Haandel, A.C., Lettinga, G., 1994. Anaerobic Sewage Treatment – A Practical Guide for Regions with a Hot Climate. John Wiley and Sons, England, pp. 226. Zaiat, M., Cabral, A.K.A., Foresti, E., 1994. Horizontal-flow anaerobic immobilized sludge reactor for wastewater treatment: conception and performance evaluation. Revista Brasileira de Engenharia 11, 33–42. Zhang, Y., Yan, L., Chi, L., Long, X., Mei, Z., Zhang, Z., 2008. Startup and operation of anaerobic EGSB reactor treating palm oil mill effluent. J. Environ. Sci. 20, 658–663.
4. Conclusions In this study, anaerobic treatment of dilute bilge water was performed by using HUASB reactor at ambient temperature. After a good resulted immobilization of sludge in the support materials and start-up period, the COD removal efficiency and oil residual concentration were promising at the end of the operation. The immobilization of the biomass in the support materials had an important role in reducing the influent COD. According to the obtained results, it can be concluded that the HUASB reactor is a promising option for the treatment of the low-strength bilge water, produced from the ships in Caspian Sea at the ambient temperatures.
Contents lists available at ScienceDirect
Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng
Short communication
Treatment of a low-strength bilge water of Caspian Sea ships by HUASB technique Seyyed Mohammad Emadian a , Morteza Hosseini b , Mostafa Rahimnejad c,d, * , Mohammad Hassan Shahavi b , Behnam Khoshandam a a
Department of Chemical Engineering, Semnan University, Semnan, Iran Department of Chemical Engineering, Babol University of Technology, Babol, Iran Biofuel & Renewable Energy Research Center, Faculty of Chemical Engineering, Babol Noshirvani University of Technology, Babol, Iran d Advanced Membrane & Biotechnology Research Center, Faculty of Chemical Engineering, Babol Noshirvani University of Technology, Babol, Iran b c
A R T I C L E I N F O
A B S T R A C T
Article history: Received 9 July 2014 Received in revised form 16 January 2015 Accepted 5 April 2015 Available online xxx
Oily bilge water is one of the major pollutants that threats marine environment due to its direct discharge from ships into sea. The aim of this paper is to investigate the possibility of dilute bilge water treatment by using hybrid up-flow anaerobic sludge blanket (HUASB) bio-reactor. The reactor operated at two hydraulic retention times (HRTs) of 10 h and 8 h. The organic loading rate (OLR) was gradually increased from 0.12 g to 0.6 g chemical oxygen demand (COD)/l day. After the immobilization of sludge on the surface of the support materials and 10 days of batch feeding of the reactor with the waste water as acclimation period (with COD removal of 59%), the continuous operation of the reactor started. At the end of the experiment, with the HRT of 8 h and OLR of 0.6 g COD/l day, the COD removal efficiency reached the amount of 75%. Furthermore, the bio-reactor showed a good performance in removing oil from the waste stream which was significantly lower than the standard value which has been laid down for the discharge of the bilge water from ships by the International Maritime Organization (IMO). The obtained data demonstrated that the HUASB reactor is an appropriate system for the treatment of a low-strength bilge water. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Anaerobic treatment HUASB reactor COD pH Oil content
1. Introduction Bilge water is a corrosive mixture of seawater containing a variety of constituents including cleaning agents, solvents, fuel, lubricating oils and hydraulic oils. The International Maritime Organization (IMO) regulates the discharge limit for ships which is 15 mg/l (MARPOL, 1973). Oil water separators (OWS) are usually employed to treat bilge water. OWS processes are gravity separators based on the density variation between oil and water phases. Cleaning agents in bilge water can create an emulsion of oil in water. When the emulsification takes place, buoyancy difference of oil and water is too small to be treated properly via the existing OWS technology. In recent years, several researches are conducted on bilge water treatment methods including ultrafiltration (UF), electrocoagulation and UF/photocatalytic oxidation. Peng et al. (2005) stated that
* Corresponding author. Tel.: +98 1113234204. E-mail addresses: [email protected], [email protected] (M. Rahimnejad). http://dx.doi.org/10.1016/j.ecoleng.2015.04.055 0925-8574/ ã 2015 Elsevier B.V. All rights reserved.
the microfiltration of bilge water as a pretreatment stage is desirable because used oils and particulates can block the feed channels of UF spiral. However, some reports indicated the disadvantages which associated with the application of membrane in treatment of bilge water. These disadvantages contain their relatively high cost of production due to the expensive raw materials, fouling which has a number of negative effects such as the reduction in membrane flux, additional capital and maintenance cost because of membrane replacement and regeneration. Karakulski et al. (1998) used a laboratory-scale ultrafiltration pilot plant with tubular membranes for the treatment of bilge water. However, the use of additional photo catalytic oxidation stage was necessary to eliminate the residual oil. Rincon and La Motta, (2014) investigated the treatment of synthetic ship bilge water in an electrocoagulation system. They concluded that the electrocoagulation process was an effective method in destabilizing of oil in water emulsions and removing the heavy metals. However, the authors applied additional flotation method to improve the treatment performance. Sun et al. (2010) investigated on the performance of biofilm-membrane bio-reactor (MBR) for treating bilge water. Although the efficiency of the reactor in removal of
S.M. Emadian et al. / Ecological Engineering 82 (2015) 272–275
COD and oil was promising, the membrane was seriously fouled without a recycling side-stream to the bio-reactor. In this study, anaerobic treatment has been chosen because it is an efficient, simple and economical method. It is also environmentally-friendly way. The hybrid up-flow anaerobic sludge blanket (HUASB) reactor configuration has combined both suspended and fixed growth of bacteria in one reactor. It has also used the advantages of both up-flow anaerobic sludge blanket (UASB) and up-flow anaerobic fixed film (UAFF) reactors. This kind of reactor is efficient in the treatment of dilute to high strength wastewaters at low to high organic loading rates. Bilge water is classified in the low-strength group of wastewater. Although anaerobic process is used for the treatment of medium and high strength wastewaters, it has already been applied successfully for a number of waste streams including low-strength wastewaters. Also, the efficiency of HUASB reactor (on the basis of COD and oil removal) in treatment of low-strength bilge water under different low organic loading rates has been studied.
273
the sample surface. The sample surface was also collected in a closed bottle. 2.4. Analytical methods Several monitoring parameters were evaluated during the entire operation, including COD and oil concentrations, as well as pH and temperature. For COD analysis, HACH’s Method 8000, a combination of reactor digestion method and colorimetric method, was used (DR/890, 2009). This method is equivalent to standard method 5220D: closed reflux, colorimetric method (APHA, 2008). Analysis of oil was determined according to USEPA 1664 and n-hexane gravimetric methods. Temperature and pH were measured by using a pH/temperature probe (HANNA, PH212, Germany) with automatic temperature compensation. The method used in pH measurement was generally in compliance with Standard Method 4500B (APHA, 2008). 2.5. Start-up and operation scheme
2. Material and methods
2.2. Wastewater characteristics The bilge water was collected from the ships which had anchored at Amirabad port, Behshahr, Mazandaran, Iran. The HUASB reactor was fed with bilge water pre-settled for 10 min. The characteristics of pre-settled bilge water were as follows: pH: 8–9, COD: 20–200 mg/l, total solid (TS): (800–2400) mg/l, TSS: 220–1760 mg/l, total nitrogen: 836 mg/l and total phosphorus (TP): 211 mg/l (TN and TP were measured in COD = 50 mg/l). The pH of the feed was adjusted to 6.8–7.2 by adding diluted HCl. The only supplementary nutrient, MgNO3, was added to yield a COD (N ratio of 250:5) as a nitrogen supply.
250
start-up-
later opration
0.9
200
0.75 0.6
150
0.45
100
2.3. Inoculum (seed sludge)
0.3 50
The reactor was seeded with a mixture of activated sludge from the aerobic wastewater treatment of the Mazandaran pulp, paper industry and a non-granular sludge obtained from a UASB reactor operating with cheese whey wastewater from the Gela food industry of Amol, Mazandaran, Iran. The TSS of the mixture was 13 g/l. The non-granular sludge was methanogenically active as the biogas bubbles which were apparently observed from stripping of
0.15
0
0 1
21
41
61 81 101 121 Operation time (day)
Influent COD
HRT
141 OLR
Fig. 1. Start-up and operation scheme for UASFF reactor.
OLR (g COD/l day)
The fabricated Plexiglass reactor column with an internal diameter of 4.4 cm and a liquid height of 194 cm was used. The column included three sections: bottom, middle and top sections. The bottom part of the column, with a volume of 1823 ml operated as a UASB reactor whereas the middle part of the column with a volume of 855 ml was used as a fixed film reactor. The top part of the bio-reactor with a volume of 273 ml was an unpacked column prior to the effluent overflow. The fixed film section of the column was randomly packed with 270 billowy pieces of PVC rings which had a diameter of 15 mm. The height of each ring was equal to 13 mm (150 m2/m3 specific surface areas for each one). The media in the reactor were stabled by using a plastic mesh. The wastewater as a substrate was continuously fed to the base of the reactor which was located under the bed of active sludge and through a T-inlet connected to a peristaltic pump. An outlet was provided at the top of the reactor that was connected to a 1 l funnel shaped settling compartment served as a sedimentation part where the final effluent was collected from the top of this tank. The reactor operated at ambient temperature (15–25 C).
Start-up period is usually a time consuming period. In order to decrease the time, the immobilization of biomass on the support material was done; therefore, the mentioned mixture of sludge was used by means of a technique described by Zaiat et al. (1994). The support material together with the sludge was stored in 1.5 l closed bottle and homogenized for the period of a week so as to secure steadier immobilization of bio-particles in the supporting material. After this stage, the packing material filled in its place in the HUASB reactor. The reactor was inoculated with 500 ml of the same sludge mixture. In order to acclimatize the sludge with bilge water, the daily batch feed reactor with the bilge water (50 mg/l) was selected for 10 days. After each feed, the liquid content of the reactor was continuously circulated for 1 day (until the next feed). The acclimation period permitted oxygen level to decrease to prevent inhibition of anaerobic bacteria as well as the bacteria population to adjust with the feed wastewater. The TSS concentration of the sludge after the 10-day batch-fed period was 16.5 g/l. A COD removal efficiency of about 59% was achieved at the end of this acclimation period. The start-up was carried out by using stepped organic loading to produce the most rapid biomass development. The HRT of 10 h was kept constant throughout the start-up duration and the OLR increased from 0.12 g to 0.24 g COD/l day. The reactor was allowed to reach steady state condition before each OLR change. When effluent COD reached a relatively constant value, the steady state condition was achieved and then influent OLR can be raised. The experimental procedure has been illustrated in Fig. 1.
Influent COD (mg/l) HRT (h)
2.1. Experimental apparatus
274
3. Results and discussion 3.1. Bio-reactor performance 3.1.1. pH Changes in acidity (pH) of the effluent from the HUASB reactor during the operation has been shown in Fig. 2. As it is shown in Fig. 2, the pH was comparatively stable (varying from 8.04 to 8.78) during the operation, which was suitable for efficient methanogenesis. This indicated that the system had sufficient alkalinity to neutralize organic acids coming from the hydrolysis and fermentation stage. One can see in Fig. 2 that there are numbers of decrease in pH through the operation attributed to the accumulation of the produced volatile fatty acid (VFA) due to enhancement of the influent OLR. Accumulation of VFA in the reactor did not sour the reactor. The similar result was reported by Van Haandel and Lettinga (1994) which was about the treatment of domestic wastewater. There was a sudden decrease in pH from 8.52 at day of 96 to 8.1 at day of 111 because the effect of the nutrient was tested at this stage of the operation. For testing this effect, from day of 96 to day of 101, the addition of the nutrient was ceased and after that the new nutrient, NH4Cl, was added to the reactor till day of 111. In this period of the operation, decrease in pH connected to the lower activity of the methanogenic bacteria which is responsible for consuming of the VFA. However, the reactor recovered itself because of reintroducing of MgNO3 as the nutrient to the reactor and pH increased again which is indicative of the increment in methanogenic bacteria activity. 3.2. COD removal efficiency The bio-reactor performance during the operation is shown in Fig. 3. The reactor was fed with an influent COD of 50 mg/l and 100 mg/l during the start-up stage. As it is shown in Fig. 3, the COD removal efficiency increased from 40% at the beginning of the start-up to 75% at the end of the operation implying that the sludge was acclimated appropriately to the bilge water. Each increment in OLR during the operation led to a reduction in COD removal efficiency. A comparison between Figs. 2 and 3 shows a similar trend between effluent pH and COD removal efficiency which concurs with results obtained by Zhang et al. (2008). The sudden
Effluent pH
0.8
start-up
9.3
later operation
9.1
0.7 0.6
8.9 8.7
0.5
8.5
0.4
8.3
0.3
8.1
100 80 60 40 20 0 1
21
41
61
81
101
121
141
Operating time (day) Influent COD
Effluent COD
COD Removal
Fig. 3. Bioreactor performance during operation.
decrease is attributed to the more VFA production due to the introduction of new OLR to the reactor. Similar observation was reported by other authors. The system recovered shortly and adapted to the new condition with time. Additionally, it is clearly understood that the initial immobilization of microorganisms on the surface of the support materials had a key role in shortening the start-up procedure. As it was mentioned before, the effect of the nutrient on the performance of the reactor was tested during the days of 96–111. According to Fig. 3, the COD removal efficiency decreased from 77% to 42% during the days of 96–101. In this period, adding MgNO3 to the reactor was ceased. After that, by addition of new nutrient (NH4Cl) to the reactor, the COD removal efficiency showed a little increase and reached an amount of 50% at the day of 111. Therefore, MgNO3 was reintroduced to the reactor from day of 111. By increasing the COD influent and reintroducing MgNO3 as the nutrient to the reactor, the COD removal efficiency raised again and it reached an amount of the 75% at the end of the study which was much higher than the result was obtained by Sun et al. (2010). They reported that the COD removal efficiency of moving biofilm bioreactor (an aerobic bio-reactor) in treating shipboard wastewater (including synthetic bilge water) was about 59% in HRT of 8 h. For improving the performance of the bio-reactor, they applied a membrane as a post treatment stage with a recycle-stream to the bio-reactor (Sun et al., 2010). The TSS concentration of the sludge in the reactor increased from 16.5 g/l at the beginning of the start-up to 67 g/l at the end of the study so that the sludge acted as a filter for removing the suspended solids from the wastewater. Subsequently, the UASB reactor had a noticeable effect on removing the TSS content of the wastewater.
OLR (g COD/l.day)
9.5
120
later operation
start-up
220 200 180 160 140 120 100 80 60 40 20 0
0.2
7.9
0.1
7.7 7.5
0 1
21
41 61 81 101 121 141 Operating time (day) pH
OLR
Fig. 2. Change of pH during operation.
COD removal efficiency (%)
During the experiment, COD reduction and pH were monitored daily. Also, oil reduction was checked 2 times throughout the experiment, firstly after the end of the start-up period. The second check was also after the completion of the whole experiment.
Influent and Effluent COD (mg/l)
S.M. Emadian et al. / Ecological Engineering 82 (2015) 272–275
Fig. 4. Oil removal at two point of operation.
S.M. Emadian et al. / Ecological Engineering 82 (2015) 272–275
275
3.3. Oil content
References
The reduction of oil content for the wastewater at the end of start-up and operation of the reactor has been shown in Fig. 4. It can be seen in Fig. 4 that either at the end of the start-up or the operation, the oil effluent concentration was below 15 mg/l which is a standard level for discharging the wastewater from ships (MARPOL, 1973). Sun et al. (2010) obtained that the residual oil concentration of about 30 mg/l from the effluent of the MBBR reactor in HRT of 8 h which was double times higher than the standard level (15 mg/l).
APHA, 2008. Standard Methods for the examination of Water and Wastewater. American Public Health Association/American Water Work Association/Water Environmental Federation, Washington, DC. DR/890, 2009. colorimeter, Procedures Manual, Method 8000. in: Hach Company L., CO, ed. Karakulski, K., Morawski, W.A., Grzechulska, J., 1998. Purification of bilge water by hybrid ultrafiltration and photocatalytic processes. Sep. Purif. Technol. 14, 163–173. MARPOL, 1973. International Convention for the Prevention of Pollution from Ships, 1973, as modified by the protocol of 1978 relating thereto (MARPOL 73/78). in: (IMO) I.M.O., ed. Peng, H., Tremblay, A.Y., Veinot, D.E., 2005. The use of backflushed coalescing microfilteration as pretreatment for the ultrafilteration of bilge water. Desalination 181, 109–120. Rincon, G.J., La Motta, E.J., 2014. Simultaneous removal of oil and grease, and heavy metals from artificial bilge water using electrocoagulation/flotation. J. Environ. Manage. 144, 42–50. Sun, C., Leiknes, T., Weitzenbock, J., Thorstensen, B., 2010. Development of an integrated shipboard wastewater treatment system using biofilm-MBR. Sep. Purif. Technol. 75, 22–31. Van Haandel, A.C., Lettinga, G., 1994. Anaerobic Sewage Treatment – A Practical Guide for Regions with a Hot Climate. John Wiley and Sons, England, pp. 226. Zaiat, M., Cabral, A.K.A., Foresti, E., 1994. Horizontal-flow anaerobic immobilized sludge reactor for wastewater treatment: conception and performance evaluation. Revista Brasileira de Engenharia 11, 33–42. Zhang, Y., Yan, L., Chi, L., Long, X., Mei, Z., Zhang, Z., 2008. Startup and operation of anaerobic EGSB reactor treating palm oil mill effluent. J. Environ. Sci. 20, 658–663.
4. Conclusions In this study, anaerobic treatment of dilute bilge water was performed by using HUASB reactor at ambient temperature. After a good resulted immobilization of sludge in the support materials and start-up period, the COD removal efficiency and oil residual concentration were promising at the end of the operation. The immobilization of the biomass in the support materials had an important role in reducing the influent COD. According to the obtained results, it can be concluded that the HUASB reactor is a promising option for the treatment of the low-strength bilge water, produced from the ships in Caspian Sea at the ambient temperatures.