Anaerobic membrane reactor with phase separation for the treatment of cheese whey

Two-phase anaerobic digestion of cheese whey was investigated in a system consisting of a stirred acidogenic reactor followed by a stirred methanogenic reactor, the latter being coupled to a membrane filtration system to enable removal of soluble effluent whilst retaining solids. The acidogenic reactor was operated at a hydraulic retention time (HRT) of one day, giving maximum acidification of 52.25% with up to 5 g/l volatile fatty acids, of which 63.7% was acetic acid and 24.7% was propionic acid. The methanogenic reactor received an organic load up to 19.78 g COD/ld, corresponding to a HRT of 4 days, at which 79% CODs and 83% BOD(5) removal efficiencies were obtained. Average removals of COD, BOD(5) and TSS in the two-phase anaerobic digestion process were 98.5%, 99% and 100%, respectively. The daily biogas production exceeded 10 times reactor volume and biogas methane content was greater than 70%.     

An integrated treatment system for coffee processing wastewater using anaerobic and aerobic process

The experiment was conducted to develop an integrated treatment system for coffee processing wastewater (CPWW) through the combination of biomethanation with aeration and wetland plants treatment. The biomethanation was carried out at different hydraulic retention times (HRTs) using upflow anaerobic hybrid reactor (UAHR) and 18 h of HRT was found to be optimum. The maximum biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total solids (TS) reduction were 66.0%, 61.0% and 58.0%, respectively with organic loading rate of 9.55 kg m^?3 day^?1. The reduction of pollution load of the wastewater by microbial action augmented by aeration resulted in the reduction of electrical conductivity (EC), BOD, COD, and total solids (TS). Continuous aeration of wastewater resulted in maximum reduction of BOD (74.6%), COD (68.6%) and TS (49.3%). The wetland plant, Typha latifolia reduced 85.4% and 78.0% of BOD and COD, respectively in biomethanated cum aerated CPWW.     

Start-up alternatives and performance of an UASB pilot plant treating diluted municipal wastewater at low temperature

Different start-up procedures of an upflow anaerobic sludge bed (UASB) digester were carried out. Start-up without inoculum (experiment A) was delayed for about 120 day. The digester reached 75-85% total suspended solids (TSS) removal, 54-58% total chemical oxygen demand (TCOD) removal and 63-73% biological oxygen demand (BOD5) removal at influent concentrations of 240-340 mg TCODil-1, temperatures of 13.5-15 degrees C and hydraulic retention times (HRT) of 10-11 h. Digested sludge was used as inoculum in experiment B. After the start-up period of 75 days, digester efficiencies were 58%, 41% and 54% for TSS, TCOD and BOD5 removal, respectively, working at 169 mg TCODil-1, temperature of 14 degrees C and HRT of 11 h. The sludge bed developed and stabilised quickly when using a hydraulically adapted inoculum (experiment C), but TCOD and BOD5 removals remained low and volatile fatty acids (VFA) accumulated in the effluent.     

UASB/Flash aeration enable complete treatment of municipal wastewater for reuse

A simple, efficient and cost-effective method for municipal wastewater treatment is examined in this paper. The municipal wastewater is treated using an upflow anaerobic sludge bed (UASB) reactor followed by flash aeration (FA) as the post-treatment, without implementing aerobic biological processes. The UASB reactor was operated without recycle, at hydraulic retention time (HRT) of 8 h and achieved consistent removal of BOD, COD and TSS of 60-70% for more than 12 months. The effect of FA on UASB effluent post-treatment was studied at different HRT (15, 30 and 60 min) and dissolved oxygen (DO) concentrations (low DO = 1-2 mg/L and high DO = 5-6 mg/L). The optimum conditions for BOD, COD and sulfide removal were 30-60 min HRT and high DO concentration inside the FA tank. The final effluent after clarification was characterized by BOD and COD values of 28-35 and 50-58 mg/L, respectively. Sulfides were removed by more than 80%, but the fecal coliform only by ~2 log. The UASB followed by FA is a simple and efficient process for municipal wastewater treatment, except for fecal coliform, enabling water and nutrients recycling to agriculture.     

Treatment of low strength complex wastewater using an anaerobic baffled reactor (ABR)

Treatment of a low strength complex wastewater of chemical oxygen demand (COD) around 500mg/L was studied in a 10L capacity laboratory scale anaerobic baffled reactor (ABR). It was operated at hydraulic retention times (HRTs) of 20, 15, 10, 8 and 6h. Corresponding organic loading rates (OLRs) were 0.6, 0.8, 1.2, 1.5 and 2kg COD/m(3)d. At every HRT (or OLR), pseudo steady state (PSS) was achieved. Even at maximum OLR of 2kg COD/m(3)d, COD and biochemical oxygen demand (BOD) removals exceeded 88%. Removal of particulate fraction of organics was found to be greater than soluble fraction. Compartment-wise studies of various parameters revealed that if the OLR was larger, the number of initial compartments played significant role in the removal of organics. The values of volatile fatty acids (VFA) demonstrated that hydrolysis and acidogenesis were the main biochemical activities in the initial few compartments. Based on the tracer studies, dead space in the ABR was found to range from 23% to 34%. The flow pattern in the ABR was classified as intermediate between plug flow and perfectly mixed flows. Observations from scanning electron micrographs (SEM) also suggested that distinct phase separation takes place in an ABR. Study of organic and hydraulic shock loads revealed that ABR was capable of sustaining the type of shock loads generally experienced at a sewage treatment plant (STP).     

Anaerobic treatment of low-strength municipal wastewater by a two-stage pilot plant under psychrophilic conditions

A two-stage anaerobic treatment pilot plant was tested for the treatment of raw domestic wastewater under temperatures ranging from 21 to 14 degrees C. The plant consisted of a hydrolytic upflow sludge bed (HUSB) digester (25.5m3) followed by an upflow anaerobic sludge blanket (UASB) digester (20.36m3). The hydraulic retention time (HRT) varied from 5.7 to 2.8h for the first stage (HUSB digester) and from 13.9 to 6.5h for the second stage (UASB digester). Total suspended solids (TSS), total chemical oxygen demand (TCOD), and biochemical oxygen demand (BOD) removals ranged from 76% to 89%, from 49% to 65%, and from 50% to 77%, respectively, for the overall system. The percentage of influent COD converted to methane was 36.1%, the hydrolysis of influent volatile suspended solids (VSS) reached 59.7% and excess biomass was 21.6% of the incoming VSS. Plant performance was influenced by the wastewater concentration and temperature, yet better results were obtained for influent COD higher than 250mg/l.     

Operational factors and nutrient effects on activated sludge treatment of Pinus radiata kraft mill wastewater

The biodegradability of Pinus radiata bleached kraft mill wastewater by an activated sludge treatment during a period of 280 days was evaluated. The effect of varying hydraulic retention time (HRT) in the range of 48 to 4.5 h and nitrogen (N) and phosphorus (P) addition on removal of biological oxygen demand (BOD5), chemical oxygen demand (COD), suspended solids (TSS and VSS), total phenolic compounds, tannin and lignin and reduction of toxicity was investigated. Removal of BOD5 was higher than 90% when HRT varied from 16 to 6 h, but decreased when HRT was less than 6 h. Similar performance was observed for COD removal, which was about 60% when HRT was varied from 16 to 6 h. Removal of total phenolic compounds and tannin and lignin was seriously affected by HRT. N and P addition to maintaining a ratio of 100:5:0.3 provided optimal BOD5, COD and suspended solids removal when HRT varied from 16 to 7 h, and no toxicity (using Daphnia) was detected in the treated effluent. When HRT was less than 6 h, the system showed destabilisation and pH, COD, BOD5 and suspended solids removal decreased.     

Start-up of an UASB-septic tank for community on-site treatment of strong domestic sewage

Two community on-site UASB-septic tanks were operated in parallel over a six months period under two different hydraulic retention times (HRT) of 2 days for R1 and 4 days for R2 at mean sewage temperature of 24 degrees C. The sewage was characterised by a high COD(tot) concentration of 1189 mg/L, with a large fraction of COD(sus), viz. 54%. The achieved removal efficiencies in R1 and R2 for COD(tot), COD(sus), BOD5 and TSS were "56%, 87%, 59% and 81%" and "58%, 90%, 60% and 82%" for both systems, respectively. R2 achieved a marginal but significant (p<0.05) better removal efficiencies of those parameters as compared to R1. The COD(col) and COD(dis) removals in R1 and R2 were respectively 31% and 20%, and 34% and 22%. The sludge accumulation was very low suggesting that the desludging frequency will be of several years. Accordingly, the reactor can be adequately designed at 2 days HRT.     

Ambient temperature treatment of low strength wastewater using anaerobic sequencing batch reactor

Low strength wastewater having chemical oxygen demands (COD) concentrations of 1000, 800, 600 and 400mg/l were treated at 35, 25, 20 and 15¡C using four anaerobic sequencing batch reactors (ASBRs). Reactor 1 was operated at hydraulic retention time (HRT) of 48h, reactor 2 at 24h HRT, reactor 3 at 16h HRT and reactor 4 at 12h HRT. 80 to 99% soluble COD was removed at the various operational conditions, except during 15¡C treatment of 1000 and 800mg/l COD wastewater at 12h HRT and 1000mg/l COD wastewater at 16h HRT, where excessive loss of biological solids occurred. The ASBR process can be an effective process for the treatment of low concentrated wastewaters which are usually treated aerobically with large amount of sludge production and higher energy expenditures.     

以纸为碳源去除地下水硝酸盐的研究

研究了以纸为碳源和反应介质的生物反应器对水中硝酸盐的去除。结果表明,以纸为碳源的反应器启动快．反硝化反应受温度及水力停留时间影响大。25℃的反硝化速率是14℃的1．7倍。在室温25±1℃,进水硝酸盐氮浓度为45．2mg·L^-1、水力停留时间8．6h时,反应器对硝酸盐氮的去除率在99．6％以上,当水力停留时间为7．2h,氮去除率只有50％。反硝化反应受pH值和溶解氧的影响小,反应进行过程中,纸表面形成了生物膜,纸也被消耗了．采用反应器出水再经活性炭吸附的工艺流程处理高硝酸盐氮地下水,<33．9mg·L^-1的硝酸盐氮完全去除,没有出现NC2-N,最终出水水质DOC<11mg·L^-1。     

Development of an improved anaerobic filter for municipal wastewater treatment

Development of an improved reactor configuration of anaerobic filter was carried out for the elimination of clogging of filter media. The experiments over different hydraulic retention times (HRTs) indicated that the HRT of 12 h was the most appropriate one for the system studied while treating the municipal wastewater, which resulted 90% and 95% BOD and COD reduction, respectively. Reduction up to 95% in suspended solids concentration could be achieved without any pretreatment. The specific biogas yield obtained was 0.35 m(3) CH(4)/kgCODr with 70% of CH(4) content in the biogas generated from the system at the HRT of 12 h. Operational problems such as clogging of filter media were not observed throughout the period of study over 600 d.     

Continuous fill intermittent decant type sequencing batch reactor application to upgrade the UASB treated sewage

The performance of continuous flow intermittent decant type sequencing batch (CFID) reactor treating the effluent of an UASB reactor treating domestic wastewater and operated at 8 h hydraulic retention time (HRT) was investigated. The CFID was operated at three different HRTs (22, 8 and 6 h) and three different dissolved oxygen (DO) patterns (<0.5, 2.5–3.5 and 3.5–4.5 mg/L). The highest effluent quality was observed at the 8 h HRT and 2.5–3.5 mg/L DO concentration. At this operational condition, the average BOD, TSS, ammonia nitrogen and fecal coliform removal efficiencies were 83, 90, 74 and 99 %, respectively. The CFID is a promising post-treatment option for existing UASB systems, with a final effluent quality that comply with receiving water and effluent reuse criteria.     

Treatment of sewage water from tourist areas by anaerobic fixed-bed reactor

A laboratory-scale anaerobic fixed-bed reactor, operating at ambient temperature (30 to 35°C), was used to treat sewage water from tourist areas in Cuba at hydraulic retention times (HRT) ranging from 4 to 72 h. The total chemical oxygen demand (T-COD), total biological oxygen demand (T-BOD) and total suspended solids removal varied between 30 and 80%, 40 and 95% and 25 and 80%, respectively. Total and faecal coliforms were reduced by 98.1 to 99.9% and by 99.0% to 99.9% respectively, despite the marked decrease in HRT from 72 to 4 h.     

Treatment of screened dairy manure by upflow anaerobic fixed bed reactors packed with waste tyre rubber and a combination of waste tyre rubber and zeolite: effect of the hydraulic retention time

Two laboratory-scale anaerobic fixed bed reactors were evaluated while treating dairy manure at upflow mode and semicontinuous feeding. One reactor was packed with a combination of waste tyre rubber and zeolite (R1) while the other had only waste tyre rubber as a microorganism immobilization support (R2). Effluent quality improved when the hydraulic retention time (HRT) increased from 1.0 to 5.5 days. Higher COD, BOD5, total and volatile solids removal efficiencies were always achieved in the reactor R1. No clogging was observed during the operation period. Methane yield was also a function of the HRT and of the type of support used, and was 12.5% and 40% higher in reactor R1 than in R2 for HRTs of 5.5 and 1.0 days, respectively. The results obtained demonstrated that this type of reactor is capable of operating with dairy manure at a HRT 5 times lower than that used in a conventional reactor.     

Biological treatment of acid dyeing wastewater using a sequential anaerobic/aerobic reactor system

The treatment of the wastewater taken from a wool dyeing processing in a wool manufacturing plant was investigated using an anaerobic/aerobic sequential system. The process units consisted of an anaerobic UASB reactor and an aerobic CSTR reactor. Glucose, alkalinity and azo dyes were added to the raw acid dyeing wastewater in order to simulate the dye industry wastewater since the raw wastewater contained low levels of carbon, NaHCO₃ and color through anaerobic/aerobic sequential treatment. The UASB reactor gave COD and color removals of 51–84% and 81–96%, respectively, at a HRT of 17 h. The COD and color removal efficiencies of the UASB/CSTR sequential reactor system were 97–83% and 87–80%, respectively, at a hydraulic retention time (HRTs) of 3.3 days. The aromatic amines (TAA) formed in the anaerobic stage were effectively removed in the aerobic stage.     

Performance of subsurface flow constructed wetland taking pretreated swine effluent under heavy loads

Subsurface flow constructed wetlands (SSFCW) subjected to changing of loading rates are poorly understood, especially when used to treat swine waste under heavy loads. This study employed a SSFCW system to take pretreated swine effluent at three hydraulic retention times (HRT): 8.5-day HRT (Phase I), 4.3-day HRT (Phase II), and 14.7-day HRT (Phase III). Results showed that the system responded well to the changing hydraulic loads in removing suspended solids (SS) and carbonaceous oxygen demands. The averaged reduction efficiencies for four major constituents in the three phases were: SS 96-99%, chemical oxygen demand (COD) 77-84%, total phosphorus 47-59%, and total nitrogen (TN) 10-24%. While physical mechanisms were dominant in removing pollutants, the contributions of microbial mechanisms increased with the duration of wetland use, achieving 48% of COD removed and 16% of TN removed in the last phase. Water hyacinth made only a minimal contribution to the removal of nutrients. This study suggested that the effluent from SSFCW was appropriate for further treatment in land applications for nutrient assimilation.     

Rapid formation of hydrogen-producing granules in an anaerobic continuous stirred tank reactor induced by acid incubation

A novel approach to rapidly initiate granulation of hydrogen-producing sludge was developed in an anaerobic continuous stirred tank reactor at 37 degrees C. To induce microbial granulation, the acclimated culture was subject to an acid incubation for 24 h by shifting the culture pH from 5.5 to 2.0. The culture was resumed to pH 5.5 after the incubation and the reactor was operated at hydraulic retention times (HRTs) of 12, 6, 2, 1, and 0.5 h in sequence. Microbial aggregation took place immediately with the initiation of acid incubation and granules were developed at 114 h. No granule was observed in the absence of acid incubation in the control test. Changing the culture pH resulted in improvement in surface physicochemical properties of the culture favoring microbial granulation. The zeta potential increased from -11.6 to -3.5 mV, hydrophobicity in terms of contact angle improved from 31 degrees to 43 degrees and extracellular proteins/polysaccharides ratio increased from 0.2 to 0.5-0.8. Formation of granular sludge facilitated biomass retention of up to 32.2 g-VSS/L and enhanced hydrogen production. The hydrogen production rate and hydrogen yield increased with the reduction in HRT at an influent glucose concentration of 10 g/L once steady granular sludge layer was formed, achieving the respective peaks of 3.20 L/L x h and 1.81 mol-H(2)/mol-glucose at 0.5 h HRT. The experimental results suggested that acid incubation was able to initiate the rapid formation of hydrogen-producing granules by regulating the surface characteristics of microbial aggregates in a well-mixed reactor, which enhanced the hydrogen production.     

Ecological clarification of cheese whey prior to anaerobic digestion in upflow anaerobic filter

Anaerobic digestion of cheese whey wastewaters (CW) was investigated in a system consisting of an ecological pretreatment followed by upflow anaerobic filter (UAF). The pretreatment was conducted to solve the inhibition problems during anaerobic treatment of CW caused by the amounts of fats, proteins and carbohydrates and to avoid the major problems of clogging in the reactor. The optimized ecological pretreatment of diluted CW induce removal yields of 50% of chemical oxygen demand (COD) and 60% of total suspended solids (TSS) after acidification by Lactobacillus paracasei at 32 degrees C during 20 h and neutralization with lime. The pretreated CW was used to feed UAF (35 degrees C). The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the pretreated CW anaerobic degradation were examined. The average total COD removals achieved was 80-90%. The performance of the reactor was depressed by increasing the COD concentration to 20 g/l (OLR = 4 gCOD/ld) and the COD removal efficiency was reduced to 72%. Significant methane yield (280 l/kg COD removal) was obtained at an HRT of 2 days.     

Anaerobic treatment of kraft bleaching plant effluent

Anaerobic treatment of a kraft bleaching plant effluent was studied with focus on the removal of chlorinated organic compounds and biochemical O₂ demand (BOD). Experiments were carried out using a laboratory-scale anaerobic fixed-film process operated at different hydraulic retention times (HRTs). The process efficiently removed a variety of chloro-organic compounds when the HRT was 10 h or longer. However, a very long treatment time was required for significant removal of chlorofor; in fact, at the shortest HRT tested (6 h), there was a net production of chloroform. The overall removal of organically bound chlorine, measured as adsorbable organic halogens, was about 50%, and 60% removal of the extractable organic chlorine was achieved at an HRT of 15 h. About 70% of the BOD₇ and 20% of the chemical O₂ demand (COD) were removed. Up to 0.19 Nl of methane was produced per gram of COD removed by the treatment. When th HRT of the anaerobic process was shortened from 10 to 6 h, the methane production ceased. Correspondence to: Peijie Yu     

Phenol inhibition of biological nutrient removal in a four-step sequencing batch reactor

Nutrient removal from synthetic wastewater was investigated using a four-step sequencing batch reactor (SBR) at different phenol (C₆H₅OH) concentrations in order to determine the inhibition effects of phenol on biological nutrient removal. The nutrient removal process consisted of anaerobic, oxic, anoxic, and oxic phases with hydraulic residence times (HRT) of 1 h/3 h/1 h/1 h and a settling phase of 3/4 h. Solids retention time (SRT) was kept constant at 10 days in all experiments. Initial phenol concentrations were varied between 0 and 600 mg l⁻¹ at seven different levels. The effects of phenol on COD, NH₄-N, and PO₄-P removals and effluent nutrient levels were investigated. Phenol was almost completely degraded up to 400 mg l⁻¹ phenol concentration resulting in almost negligible inhibition effects on COD, NH₄-N, and PO₄-P removals. Nutrient removals were adversely affected by phenol at concentrations above 400 mg l⁻¹. Above 95% COD, 90% NH₄-N and 65% PO₄-P removal was obtained for phenol concentrations below 400 mg l⁻¹. The sludge volume index (SVI) was almost constant around 45 ml g⁻¹ for phenol concentrations below 400 mg l⁻¹ but increased to 90 ml g⁻¹ at a phenol level of 600 mg l⁻¹.