Optimization of the performance of an integrated anaerobic-aerobic system for domestic wastewater treatment

A promising system consisting of Up-flow Anaerobic Sludge Blanket (UASB) and Down-Flow Hanging Sponge (DHS) system was investigated for removal of COD, BOD(5) fractions, ammonia and faecal coliform from domestic wastewater. The combined system was operated at different HRTs of 16, 11 and 8 h. The results indicate that increasing the total HRT from 8 to 16 h significantly (p < 0.05) improves the COD(total) and BOD(5 total) removal mainly as a result of a higher removal of COD(soluble), BOD(soluble), COD(particulate) and BOD(particulate). The main part of coarse suspended solids was removed in the UASB reactor (76.4+/-18%) and the remaining portion was adsorbed and/or enmeshed and degraded in the biomass of the DHS system. The combined system achieved a substantial reduction of total suspended solids (TSS) resulting in an average overall percentage removal of 94+/-6% (HRT = 16 h) and 89.5+/-7.8% (HRT = 8 h). Faecal coliform reduction was significantly improved when increasing the total HRT from 8 to 16 h. Residual counts of faecal coliform were 3.1 x 10(3)/100 ml at a total HRT of 16 h, and 2.8 x 10(4)/100 ml at total HRT of 8 h, corresponding to overall removal efficiency of 99.97+/-0.03 and 99.6+/-0.3% respectively. Despite the increase of ammonia concentration as a result of protein hydrolysis in the UASB reactor, a substantial removal of ammonia was achieved in the DHS system. The results obtained show that decreasing the OLR imposed to DHS system from 2.6 to 1.6 kg COD/m(3).d significantly (p < 0.05) improves the removal efficiency of ammonia by a value of 29%. However, the removal efficiency of ammonia is not further increased when decreasing the OLR from 1.6 to 1.3 kg COD/m(3).d. The discharged sludge from UASB + DHS system exerts a good settling property and partially stabilized.DHS profile results have shown that the major part of COD, BOD(5), and TSS was removed in the upper part of the system, consequently, the nitrification process was occurring in the lower part of the DHS system.     

Behaviour of a full-scale expanded bed reactor with overlaid anaerobic and aerobic zones for domestic wastewater treatment.

This paper presents the behaviour of a full-scale expanded bed reactor (160 m3) with overlaid anaerobic and aerobic zones used for municipal wastewater treatment. The research was carried out in two experimental steps: anaerobic and anaerobic-aerobic conditions, and the experimental results presented in this paper refer to four months of reactor operation. In the anaerobic condition, after inoculation and 60 days of operation, the reactor treating 3.40 kg CODm(-3)d(-1) for thetaH of 2.69 h, reached mean removal efficiencies of 76% for BOD, 72% for COD, and 80% for TSS, when the effluent presented mean values of 225 mg.L(-1) of COD, 98 mg.L(-1) of BOD and 35 mg.L(-1) of TSS. Under these conditions, for nitrogen loading of 0.27 kgN.m(-3)d(-1), the reactor generated an effluent with mean N-org. of 8 mg.L(-1) and N-ammon. of 37 mg.L(-1), demonstrating high potential of ammonification. For the anaerobic-aerobic condition (118th day) the system was operated with thetaH of 5.38 h presented mean removal efficiencies of 84% for BOD, 79% for COD, 76% for TSS, and 30% for TKN. The reactor's operation time was less than two months, which was not long enough to reach nitrification. Regarding the obtained results, this research confirmed that this reactor is configured as a flexible and adequate alternative for the treatment of sewage, requiring relatively small area and only thetaH of 10 h that can be adjusted to the local circumstances.     

Effect of recirculation on organic matter removal in a hybrid constructed wetland system

This research project aimed to determine the technologically feasible and applicable wastewater treatment systems which will be constructed to solve environmental problems caused by small communities in Turkey. Pilot-scale treatment of a small community's wastewater was performed over a period of more than 2 years in order to show applicability of these systems. The present study involves removal of organic matter and suspended solids in serially operated horizontal (HFCW) and vertical (VFCW) sub-surface flow constructed wetlands. The pilot-scale wetland was constructed downstream of anaerobic reactors at the campus of TUBITAK-MRC. Anaerobically pretreated wastewater was introduced into this hybrid two-stage sub-surface flow wetland system (TSCW). Wastewater was first introduced into the horizontal sub-surface flow system and then the vertical flow system before being discharged. Recirculation of the effluent was tested in the system. When the recirculation ratio was 100%, average removal efficiencies for TSCW were 91 +/- 4% for COD, 83 +/- 10% for BOD and 96 +/- 3% for suspended solids with average effluent concentrations of 9 +/- 5 mg/L COD, 6 +/- 3 mg/L BOD and 1 mg/L for suspended solids. Comparing non-recirculation and recirculation periods, the lowest effluent concentrations were obtained with a 100% recirculation ratio. The effluent concentrations met the Turkish regulations for discharge limits of COD, BOD and TSS in each case. The study showed that a hybrid constructed wetland system with recirculation is a very effective method of obtaining very low effluent organic matter and suspended solids concentrations downstream of anaerobic pretreatment of domestic wastewaters in small communities.     

Coarse filters for pond effluent polishing: comparison of loading rates and grain sizes.

A system comprising a UASB reactor, shallow polishing ponds and shallow coarse filters, treating actual wastewater from the city of Belo Horizonte, Brazil, has been evaluated. The main focus of the research was to compare grain sizes and hydraulic loading rates in the coarse filters. Two filters operating in parallel were investigated, with the following grain sizes: Filter 1: 3 to 10 cm; Filter 2: 8 to 20 cm. Two hydraulic loading rates were tested: 0.5 and 1.0 m3/m3.d. The filter with the lower rock size had a better performance than the filter with the larger rock size in the removal of SS and, as a consequence, BOD and COD. A better performance was obtained with the hydraulic loading rate of 0.5 m3/m3.d, as compared to the rate of 1.0 m3/m3.d. The effluent quality during the period with the lower loading rate was very good for discharge into water bodies or for agricultural reuse (median effluent concentrations from Filter 1: BOD: 20 mg/L; COD: 106 mg/L; SS: 28 mg/L; E. coli: 528 MPN/100 mL).     

UASB与ABR工艺处理印染废水中试实验研究

对上流式厌氧反应器(UASB)和折流式厌氧反应器(ABR)处理难降解印染废水进行中试研究。结果表明:在厌氧反应器最佳水力停留时间为24 h条件下,UASB和ABR稳定运行2个多月,在进水COD质量浓度波动较大的情况下(ρmax=1 020.0 mg/L,ρmin=593.6 mg/L,ρ均=755.4 mg/L),UASB和ABR出水平均COD质量浓度分别为409.3 mg/L和420.9 mg/L,平均去除率分别为45.5%和43.9%。两种厌氧反应器对色度去除效果较佳,进水平均色度342倍,出水平均色度分别78倍和80倍,平均去除率分别为77.2%和76.6%。印染废水B/C由0.29分别提高到0.46和0.43,废水可生化性明显改善,UASB较ABR效果好。     

Operation of a full-scale pumped flow biofilm reactor (PFBR) under two aeration regimes

A novel technology suitable for centralised and decentralised wastewater treatment has been developed, extensively tested at laboratory-scale, and trialled at a number of sites for populations ranging from 15 to 400 population equivalents (PE). The two-reactor-tank pumped flow biofilm reactor (PFBR) is characterised by: (i) its simple construction; (ii) its ease of operation and maintenance; (iii) low operating costs; (iv) low sludge production; and (v) comprising no moving parts or compressors, other than hydraulic pumps. By operating the system in a sequencing batch biofilm reactor (SBBR) mode, the following treatment can be achieved: 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and total suspended solids (TSS) reduction; nitrification and denitrification. During a 100-day full-scale plant study treating municipal wastewater and operating at 165 PE and 200 PE (Experiments 1 and 2, respectively), maximum average removals of 94% BOD5, 86% TSS and 80% ammonium-nitrogen (NH4-N) were achieved. During the latter part of Experiment 2, effluent concentrations averaged: 14 mg BOD5/l; 32 mg COD(filtered)/l; 14 mg TSS/l; 4.4 mg NH4-N/l; and 4.0 mg NO3-N/l (nitrate-nitrogen). The average energy consumption was 0.46-0.63 kWh/m3(treated) or 1.25-1.76 kWh/kg BOD5 removed. No maintenance was required during these experiments. The PFBR technology offers a low energy, minimal maintenance technology for the treatment of municipal wastewater.     

Upflow anaerobic sludge blanket (UASB) treatment of supernatant of cow manure by thermal pre-treatment.

Upflow anaerobic sludge blanket (UASB) methane fermentation treatment of cow manure that was subjected to screw pressing, thermal treatment and subsequent solid-liquid separation was studied. Conducting batch scale tests at temperatures between 140 and 180 degrees C, the optimal temperature for sludge settling and the color suppression was found to be between 160-170 degrees C. UASB treatment was carried out with a supernatant obtained from the thermal treatment at the optimal conditions (170 degrees C for 30 minutes) and polymer-dosed solid-liquid separation. In the UASB treatment with a COD(Cr) loading of 11.7 kg/m3/d and water temperature of 32.2 degrees C, the COD(Cr) level dropped from 16,360 mg/L in raw water to 3,940 mg/L in treated water (COD(Cr), removal rate of 75.9%), and the methane production rate per COD(Cr) was 0.187 Nm3/kg. Using wastewater thermal-treated at the optimal conditions, also a methane fermentation treatment with a continuously stirred tank reactor (CSTR) was conducted (COD(Cr) in raw water: 38,000 mg/L, hydraulic retention time (HRT): 20 days, 35 degrees C). At the COD(Cr) loading of 1.9 kg/m3/d, the methane production rate per COD(Cr), was 0.153 Nm3/kg. This result shows that UASB treatment using thermal pre-treatment provides a COD(Cr), loading of four times or more and a methane production rate of 1.3 times higher than the CSTR treatment.     

Anaerobic treatment of Hong Kong leachate followed by chemical oxidation.

Landfill leachate of Hong Kong was first treated by the upflow anaerobic sludge blanket (UASB) process. At 37 degrees C, pH 7.1-8.5 and a HRT of 5.1-6.6 days, the process removed 66-90% of COD in the leachate for loading rates of 1-2.4 g-COD/l day depending on the strength of landfill leachate. The final effluent contained 1440-1910 mg-COD/l and 70-91 mg-BOD/l. About 92.5% of the total COD removed was converted to methane and the rest was converted to biomass with an average net growth yield of 0.053 g-VSS/g-COD-removed. The granules developed in the UASB reactor were 0.5-1.5 mm in size and exhibited good settleability. The UASB effluent was then further polished by two oxidation processes. The UASB-ozonation process removed 93.0% of the 12900 mg/l of COD from the raw leachate. The UASB-Fenton-ozonation process improved the COD removal efficiency to 99.3%. The final effluent had only 85 mg/l of COD and 10 mg/l of BOD5. Ozonation was most effectively conducted at pH 7-8 with the addition of 300 mg/l of H2O2 and for the duration of 30 min. Ozonation also significantly improved the biodegradability of the organic residues. Nearly 50% of these residues could be used as carbon source in denitrification.     

Comparison of bioreactors with different kinds of submerged packed beds for domestic wastewater treatment

The performance of aerobic submerged packed bed reactors was studied for the treatment of domestic wastewater using different kinds of packing materials with high specific areas (760-1,200 m(2)/m(3)). The tested materials were ceramic spheres, crushed tezontle, grains of high density polyethylene (HDPE), of low density polyethylene (LDPE) and of polypropylene (PP), cubes of polyurethane (PU) and polyethylene tape (SESSIL). The bioreactors were operated in continuous regime, applying organic loads in the range of 0.8-6.0 g COD.m(-2).d(-1). The obtained specific COD removal rates were very similar in all the reactors when they were operated at organic loads up to 2.0 g COD.m(-2).d(-1), after which differences in effectiveness appeared and the best results were determined in the reactors with SESSIL, LDPE and PU. Very low TSS, O&G and turbidity were obtained in all the effluents. The NH(3)-N and TN removals were dependent on the dissolved oxygen (DO) concentration and the removals at DO of 5 mg/l were 84-99% and 61-74% respectively. The best removals were determined in the reactors with PU, SESSIL and LDPE. The reactor with tezontle had also a good performance when operated with loads up to 1.0 g TN.m(-2).d(-1). The best phosphate removals (38-49%) were obtained in the reactors with PU, tezontle, ceramic sheres and SESSIL.     

Runoff quality and pollution loadings from a tropical urban catchment.

Runoff quality draining from 17.14 km2 urban catchment in Johor Bahru, Malaysia, was analysed. The land-use consists of residential (30.3%), agricultural (27.3%), open space (27.9%), industrial (8.1%) and commercial (6.4%) areas. Three storm events were sampled in detail. These storms produced stormflow between 0.84 mm and 27.82 mm, and peakflow from 2.19 m3/s to 42.36 m3/s. Water quality showed marked variation during storms especially for TSS, BOD and COD with maximum concentrations of 778 mg/l, 135 mg/l and 358 mg/l, respectively. Concentrations of TOC, DOC, NH3-N, Fe and level of colour were also high. In general, the river quality is badly polluted and falls in Class V based on the Malaysian Interim National Water Quality Standards. Event Mean Concentrations (EMC) for various parameters varied considerably between storms. The largest storm produced higher EMC for TSS, NO3-N and SS whereas the smaller storms tend to register higher EMC for BOD, COD, NH3-N, TOC, Ca, K, Mg, Fe and Zn. Such variations could be explained in terms of pollutant availability and the effects of flushing and dilution. Based on a three-month average recurrence interval (ARI) of rainfall, the estimated event loadings (ton/ha) of TSS, BOD, COD, TOC, NH3-N and NO3-N were 0.055, 0.016, 0.012, 0.039, 0.010, 0.0007 and 0.0002, respectively. Heavy metals present in trace quantities. Storms with 3 months ARI could capture about 70% of the total annual loads of major pollutants.     

The effect of operational conditions on the performance of UASB reactors for domestic wastewater treatment.

In this investigation, the performance of Upflow Anaerobic Sludge Blanket (UASB) reactors treating municipal wastewater was evaluated on the basis of: (i) COD removal efficiency, (ii) effluent variability, and (iii) pH stability. The experiments were performed using 8 pilot-scale UASB reactors (120 L) from which some of them were operated with different influent COD (CODInf ranging from 92 to 816 mg/L) and some at different hydraulic retention time (HRT ranging from 1 to 6 h). The results show that decreasing the CODInf, or lowering the HRT, leads to decreased efficiencies and increased effluent variability. During this experiment, the reactors could treat efficiently sewage with concentration as low as 200 mg COD/L. They could also be operated satisfactorily at an HRT as low as 2 hours, without problems of operational stability. The maximum COD removal efficiency can be achieved at CODInf exceeding 300 mg/L and HRT of 6h.     

Biodegradability enhancement of municipal landfill leachate

The method of enhancing the biodegradability of landfill leachate via air stripping followed by coagulation/ultrafiltration （UF） processes is introduced. In this study, the air stripping process obtained a removal efficiency of 88.6% for ammonia nitrogen （NH3-N）, at an air-to-liquid ratio （A/L） of 3 300 （pH = 11） and after 18 h of stripping. The single coagulation process increased the BOD （biological oxygen demand）/COD （chemical oxygen demand） ratio by 0.089 with a FeCl3 dosage of 570 mg/L, at pH 7.0, and the single UF process increased the BOD/COD ratio from 0.049 to 0.311. However, the combination of coagulation and UF increased the BOD/COD ratio from 0.049 to 0.423, and the final BOD, COD, NH3-N, and colour of the leachate were 1 023 mg/L, 2 845 mg/L, 145 mg/L, and 2 056, respectively, when a 3 kDa molecular weight cut-off （MWCO） membrane was used at an operating pressure of 0.7 MPa. In the ultrafiltration process, the average solution flux （Jv）, concentration multiple （Mc）, and retention rate （R） for the COD were 107.3 L/（m^2·h）, 6.3, and 84.2%, respectively.     

Evaluation of sludge properties in a pilot-scale UASB reactor for sewage treatment in a temperate region

In this study, continuous operation of a pilot-scale upflow anaerobic sludge blanket (UASB) reactor for sewage treatment was conducted for 630 days to investigate the physical and microbial characteristics of the retained sludge. The UASB reactor with a working volume of 20.2 m(3) was operated at ambient temperature (16-29 °C) and seeded with digested sludge. After 180 days of operation, when the sewage temperature had dropped to 20 °C or lower, the removal efficiency of both total suspended solids (TSS) and total biochemical oxygen demand (BOD) deteriorated due to washout of retained sludge. At low temperature, the cellulose concentration of the UASB sludge increased owing to the rate limitation of the hydrolytic reaction of suspended solids in the sewage. However, after an improvement in sludge retention (settleability and concentration) in the UASB reactor, the process performance stabilized and gave sufficient results (68% of TSS removal, 75% of total BOD removal) at an hydraulic retention time (HRT) of 9.7 h. The methanogenic activity of the retained sludge significantly increased after day 246 due to the accumulation of Methanosaeta and Methanobacterium following the improvement in sludge retention in the UASB reactor. Acid-forming bacteria from phylum Bacteroidetes were detected at high frequency; thus, these bacteria may have an important role in suspended solids degradation.     

Low-temperature post-treatment of anaerobically treated-sewage in anaerobic filter with cationic-polymer addition.

The post-treatment of domestic sewage pretreated in a 6 m3 UASB was investigated in two high-rate anaerobic filter (AF) reactors operated in parallel. The difference between the two AF reactors was only the addition of cationic polymer to the second reactor (AF + P). The reactors were operated at low temperatures, ranged between 13 and 20 degrees C. The media in each AF reactor consisted of vertical sheets of reticulated-polyurethane foam (RPF) with knobs. The results demonstrated that the AF + P reactor (HRT = 3 h) with cationic polymer addition (2 mg/L) was an efficient system for post-treatment. The removal efficiencies for total, suspended, colloidal and dissolved COD were, respectively, 41, 86 and 76 and 12% in the AF + P reactor and they were, respectively, 80, 97, 77 and 66% in the UASB + (AF + P) system. The removal of total, suspended and colloidal COD in the UASB + (AF + P) system were significantly higher than those achieved in the UASB + AF system. As hardly any nutrient was removed in the UASB + (AF + P) system, the effluent after pathogen removal is a valuable product for irrigation and fertilisation to close the water and nutrients cycle.     

Combined biological and physico-chemical treatment of baker's yeast wastewater including removal of coloured and recalcitrant to biodegradation pollutants.

The UASB reactor (35 degrees C) was quite efficient for removal of bulk COD (62-67%) even for such high strength and recalcitrant wastewater as the cultivation medium from the first separation process of baker'syeasts (the average organic loading rates varied from 3.7 to 10.3 g COD/l/d). The aerobic-anoxic biofilter (20 degrees C) can be used for removal of remaining BOD and ammonia from strong nitrogenous anaerobic effluents; however, it suffered from COD-deficiency to fulfil denitrification requirements. To balance the COD/N ratio, some bypass of raw wastewater should be added to the biofilter feed. The application of iron chloride coagulation for post-treatment of aerobic effluents may fulfil the discharge limits (even for colour mainly exerted by hardly biodegradable melanoidins) under iron concentrations around 200 mg/l.     

Kinetic study of slaughterhouse wastewater treatment by electrocoagulation using Fe electrodes

In this study, treatment of slaughterhouse wastewater by electrocoagulation was investigated in batch system using Fe electrodes. The effect of various variables such as electrode number, current density and operating time was tested. Pollutant removal efficiency increased with increasing electrode number and operating time. The biochemical oxygen demand (BOD(5))(,) chemical oxygen demand (COD), total suspended solid (TSS), and total nitrogen (TN) removal efficiencies using eight electrodes at a contact time of 50 min and a current density of 10 A/m(2) were 66, 62, 60, and 56%, respectively. Higher electrode numbers will allow shorter operating times to achieve certain removal efficiencies. Also, removal efficiencies increased by increasing the current density; the highest removal efficiencies of BOD(5,) COD, TSS, and TN at a contact time of 50 min and a current density of 25 A/m(2) were 97, 93, 81, and 84%, respectively. The results also show that the reactor pH varies directly with the current density; at 25 A/m(2), the reactor pH increased from an initial value of 7.1 to 7.7 after 50 min. The experimental results showed that the kinetics of BOD(5), COD, TSS and TN removal could be fitted adequately using a first order kinetic model (higher R(2)).     

Reliability analysis of stabilisation pond systems.

This article presents a reliability analysis of 116 full-scale pond systems in Brazil, comprising 73 primary facultative ponds and 43 anaerobic -facultative pond systems. A methodology developed by Niku et al. (1979) is used for the determination of the coefficients of reliability, in terms of the compliance of effluent BOD, COD, TSS and FC to discharge standards or effluent quality targets. The design concentrations necessary to meet the prevailing discharge standards and the expected compliance percentages have been calculated from the coefficients of reliability obtained. The results showed that few units, under the observed operating conditions, would be able to present reliable performances in terms of compliance with the analyzed standards. For the four constituents (BOD, COD, TSS and FC) and both systems (facultative ponds and anaerobic-facultative systems), the variability of the effluent quality was very large, leading to a high variability of the coefficient of variation (CV) and the coefficient of reliability (COR). The effluent quality from the facultative ponds showed a larger distance to both the desired values and the discharge standard values, compared with the anaerobic-facultative systems.     

Combined biological and physico-chemical treatment of baker's yeast wastewater.

The UASB reactor (35 degrees C) was quite efficient for removal of bulk COD (52-74%) from the raw and diluted cultivation medium from the first separation process of baker's yeasts (the average organic loading rates varied in the range 3.7-16 g COD/I/d). The aerobic-anoxic biofilter (19-23 degrees C) can be used for removal of remaining BOD and ammonia from anaerobic effluents; however, it had insufficient COD to fulfil the denitrification requirements. To balance COD/N ratio, some bypass of raw wastewater (approximately 10%) should be added to the biofilter feed. The application of iron (III)-, aluminium- or calcium-induced coagulation for post-treatment of aerobic effluents can fulfil the limits for discharge to sewerage (even for colour mainly exerted by hardly biodegradable melanoidins), however, the required amounts of coagulants were relatively high.     

Membrane bioreactor application within the treatment of high-strength textile effluent

A pilot-scale dual-stage membrane bioreactor (dsMBR) incorporating two ultra-filtration (UF) side-stream membrane modules was designed, constructed, operated and evaluated on-site for treating high-strength textile effluent. The effluent stream was characterised by a COD range of between 45 to 2,820 mg/L and an average BOD of 192.5 mg/L. The dsMBR achieved an average COD reduction of 75% with a maximum of 97% over the 9 month test period. The COD concentration obtained after dsMBR treatment averaged at 190 mg/L, which was well within the discharge standard. The average reduction in turbidity and TSS were 94% and 19.6%, respectively, during the UF-MBR stage of the system. Subsequent treatment of the UF-permeate with nanofiltration (NF) and reverse osmosis (RO) removed both the residual colour and remaining salt. A consistent reduction in the color of the incoming effluent was evident. The ADMI was reduced from an average of 659 to ～20, a lower ADMI and colour compared to the potable water. An average conductivity rejection of 91% was achieved with conductivity being reduced from an average of 7,700 to 693 μS/cm and the TDS reduced from an average of 5,700 to 473 mg/L, which facilitated an average TDS rejection of 92%.     

Simple wastewater treatment (UASB reactor, shallow polishing ponds, coarse rock filter) allowing compliance with different reuse criteria.

UASB reactors followed by polishing ponds comprise simple and economic wastewater treatment systems, capable of reaching very high removal efficiencies of pathogenic organisms, leading to the potential use of the effluent for unrestricted irrigation. However, for other types of reuse (urban and industrial), ponds are limited in the sense of producing effluents with high suspended solids (algae) concentrations. The work investigates a system with coarse rock filters for polishing the pond effluent. The overall performance of the system is analyzed, together with the potential for different types of reuse. The excellent results obtained (mean effluent concentrations: BOD: 27 mg/L; SS: 26 mg/L; E. coli: 450 MPN/100 mL) indicate the possibility of unrestricted use of the effluent for agriculture and restricted urban and industrial uses, according to WHO and USEPA.