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.     

Aerobic treatment of dairy wastewater with sequencing batch reactor systems

Performances of single-stage and two-stage sequencing batch reactor (SBR) systems were investigated for treating dairy wastewater. A single-stage SBR system was tested with 10,000 mg/l chemical oxygen demand (COD) influent at three hydraulic retention times (HRTs) of 1, 2, and 3 days and 20,000 mg/l COD influent at four HRTs of 1, 2, 3, and 4 days. A 1-day HRT was found sufficient for treating 10,000-mg/l COD wastewater, with the removal efficiency of 80.2% COD, 63.4% total solids, 66.2% volatile solids, 75% total Kjeldahl nitrogen, and 38.3% total nitrogen from the liquid effluent. Two-day HRT was believed sufficient for treating 20,000-mg/l COD dairy wastewater if complete ammonia oxidation is not desired. However, 4-day HRT needs to be used for achieving complete ammonia oxidation. A two-stage system consisting of an SBR and a complete-mix biofilm reactor was capable of achieving complete ammonia oxidation and comparable carbon, solids, and nitrogen removal while using at least 1/3 less HRT as compared to the single SBR system.     

Some properties of a sequencing batch reactor system for removal of vat dyes

Bio-sludge from a wastewater treatment plant could be used as an adsorbent of vat dye from textile wastewater. Resting bio-sludge gave a higher adsorption capacity than dead bio-sludge. The resting bio-sludge from a textile wastewater treatment plant gave relatively high COD, BOD5 and dye adsorption capacity of 364.4 +/- 4.3, 178.0 +/- 9.0 and 50.5 +/- 1.3 mg/g of bio-sludge, respectively, in synthetic textile wastewater containing 40 mg/l Vat Yellow 1. Another advantage of the bio-sludge was that, after washing with 0.1 N NaOH solution, it was reusable without any activity loss. Through treatment with a sequencing batch reactor (SBR) system, both organic and dye in STIWW could be removed. The maximum dye (Vat Yellow 1), COD, BOD5 and TKN removal efficiencies of the SBR system under an MLSS of 2000 mg/l and an HRT of three days were 98.5 +/- 1.0%, 96.9 +/- 0.7%, 98.6 +/- 0.1% and 93.4 +/- 1.3%, respectively. Although, the dye and organic removal efficiencies of the SBR system with real textile wastewater were quite low, they could be increased by adding organic matters, especially glucose. The dye, COD, BOD5 and TKN removal efficiencies of the SBR system with glucose (0.89 g/l) supplemented textile industrial wastewater were 75.12 +/- 1.2%, 70.61 +/- 3.4%, 96.7 +/- 0.0%, and 63.2 +/- 1.1%, respectively.     

Organics, sulfates and ammonia removal from acrylic fiber manufacturing wastewater using a combined Fenton-UASB (2 phase)-SBR system

A combined Fenton-UASB (2 phase)-SBR system was employed to treat acrylic fiber manufacturing wastewater. The Chemical Oxygen Demand (COD) removal and effluent Biochemical Oxygen Demand (BOD) to COD were 65.5% and 0.529%, respectively, with the optimal Fenton conditions: ferrous was 300 mg/L; hydrogen peroxide was 500 mg/L; pH was 3.0; reaction time was 2.0 h. In two-phase UASB reactor, mesophilic operation (35±0.5 °C) was performed with hydraulic retention time (HRT) varied between 28 and 40 h. The results showed that with the HRT not less than 38 h, COD and sulfate removal were 65% and 75%, respectively. The greatest sizes of granule formed in the sulfate-reducing and methane-producing phases were 5 and 2 mm, respectively. Sulfate-reducing bacteria (SRB) accounted for 35% in the sulfate-reducing phase while methane-producing archaea (MPA) accounted for 72% in the methane-producing phase. During the SBR process, shortcut nitrification was achieved by temperature control of 30 °C.     

Thermophilic anaerobic digestion of Lurgi coal gasification wastewater in a UASB reactor

Lurgi coal gasification wastewater (LCGW) is a refractory wastewater, whose anaerobic treatment has been a severe problem due to its toxicity and poor biodegradability. Using a mesophilic (35 ± 2 °C) reactor as a control, thermophilic anaerobic digestion (55 ± 2 °C) of LCGW was investigated in a UASB reactor. After 120 days of operation, the removal of COD and total phenols by the thermophilic reactor could reach 50-55% and 50-60% respectively, at an organic loading rate of 2.5 kg COD/(m³ d) and HRT of 24 h; the corresponding efficiencies were both only 20-30% in the mesophilic reactor. After thermophilic digestion, the wastewater concentrations of the aerobic effluent COD could reach below 200 mg/L compared with around 294 mg/L if mesophilic digestion was done and around 375 mg/L if sole aerobic pretreatment was done. The results suggested that thermophilic anaerobic digestion improved significantly both anaerobic and aerobic biodegradation of LCGW.     

Textiles wastewater treatment using anoxic filter bed and biological wriggle bed-ozone biological aerated filter

In this study, the performance of the anoxic filter bed and biological wriggle bed-ozone biological aerated filter (AFB-BWB-O₃-BAF) process treating real textile dyeing wastewater was investigated. After more than 2 month process operation, the average effluent COD concentration of the AFB, BWB, O₃-BAF were 704.8 mg/L, 294.6 mg/L and 128.8 mg/L, with HRT being 8.1-7.7 h, 9.2 h and 5.45 h, respectively. Results showed that the effluent COD concentration of the AFB decreased with new carriers added and the average removal COD efficiency was 20.2%. During operation conditions, HRT of the BWB and O₃-BAF was increased, resulting in a decrease in the effluent COD concentration. However, on increasing the HRT, the COD reduction capability expressed by the unit carrier COD removal loading of the BWB reactor increased, while that of the O₃-BAF reactor decreased. This study is a beneficial attempt to utilize the AFB-BWB-O₃-BAF combine process for textile wastewater treatment.     

Treatment of coal gasification wastewater by a two-continuous UASB system with step-feed for COD and phenols removal

A two-continuous mesophilic (37 ± 2 °C) UASB system with step-feed was investigated as an attractive optimization strategy for enhancing COD and total phenols removal of the system and improving aerobic biodegradability of real coal gasification wastewater. Through the step-feed period, the maximum removal efficiencies of COD and total phenols reached 55-60% and 58-63% respectively in the system, at an influent flow distribution ratio of 0.2 and influent COD concentration of 2500 mg/L; the corresponding efficiencies were at low levels of 45-50% and 43-50% respectively at total HRT of 48 h during the single-feed period. The maximum specific methanogenic activity and substrate utilization rate were 592 ± 16 mg COD-CH₄/(gVSS d) and 89 ± 12 mg phenol/(gVSS d) during the step-feed operation. After the anaerobic digestion with step-feed, the aerobic effluent COD concentration decreased from 270 ± 9 to 215 ± 10 mg/L. The results suggested that step-feed enhanced the degradation of refractory organics in the second reactor.     

Performance evaluation of an anoxic/oxic activated sludge system: effects of mean cell residence time and anoxic hydraulic retention time

A laboratory investigation has been undertaken to asses the effects of two operating parameters, mean cell residence time (MCRT) and anoxic hydraulic retention time (HRT), on the performance of an anoxic/oxic activated sludge system. The performance of the system was evaluated in terms of its COD, nitrogen, and biomass characteristics. An activated sludge system is capable of producing a better effluent, in terms of COD and nitrogen characteristics, when it is operated in an anoxic/oxic fashion. A longer MCRT and an adequate anoxic HRT are desirable in the operation of an anoxic/oxic activated sludge system. For the wastewater used in this investigation, the anoxic/oxic unit was capable of producing an effluent with the following characteristics when it was operated at MCRT = 20 days, total system HRT = 10 h, and anoxic HRT = 3-5 h: COD = 15 mg/L; VSS = 10 mg/L; TKN = 1.30 mg/L; NH(3) - N = 0.60 mg/L; and NO(2) + NO(3) - N = 5.0 mg/L. A uniform distribution of biomass is achievable in an anoxic/oxic activated sludge system because of the intensive recirculation/convection maintained. The provision of an anoxic zone in the aeration tank promotes a rapid adsorption of feed COD into the biomass without an immediate utilization for cell synthesis. This, in turn, results in a high microbial activity and a lower observed biomass yield in the system. A tertiary treatment efficiency is achievable in an anoxic/oxic activated sludge system with only secondary treatment operations and costs. A conventional activated sludge system can be easily upgraded by converting to the anoxic/oxic operation with minor process modifications.     

Combined industrial and domestic wastewater treatment by periodic allocating water hybrid hydrolysis acidification reactor followed by SBR

A pilot-scale hybrid hydrolysis acidification reactor (HHAR) with periodic water allocation mode operation followed by sequencing batch reactor (SBR) in anoxic and aerobic metabolic function was evaluated for the treatment of low-biodegradable combined industrial and domestic wastewater. The HHAR combines the advantages of both the UASB reactor and AF, omitting the three-phase separator. Furthermore, it has lower average up-flow velocity (0.38–0.92 m/h) and higher periodic up-flow velocity (6 m/h), which made the reactor keep higher MLSS concentration (more than 10,000 mg/L) and sludge-bed is in periodic “expansion-sedimentation-expansion” state. When HRT less than 10 h, the B/C variation was positive and reached the maximum value of 0.07 at 8 h. SBR with a total cycle period of 4.5 h was applied as the post-treatment process to remove residual COD, NH₃-N and TN. At steady stage, the pilot-scale SBR effluent COD, NH₃-N and TN concentration was 65, 0.75 and 17.71 mg/L, corresponding in this case to full-scale SBR plant effluent was 93, 16.4 and 34 mg/L. Comparison results indicated that the application of HHAR–SBR system to treat combined industrial and domestic wastewater can improve effluent quality significantly.     

Improvement in post-treatment of digested swine wastewater

The performance of sequencing batch reactor (SBR) during post-treatment of digested effluent of swine wastewater was investigated. While operating SBR to treat the digested effluent directly, the performance was very poor with COD removal rate about 10%, and NH4+-N removal rate nearly 50%, with a scarce removal of total phosphorus. The performance apparently improved after adding raw swine wastewater or alkali to digested effluent. Although similar results for NH4+-N removal were achieved adopting both measures, the addition of raw wastewater proved superior in removing total nitrogen and total phosphorus. The addition of raw wastewater obtained effluent COD around 300 mg/L which was lower than that after alkali addition i.e. around 550 mg/L. Judged from the investment, oxygen demand, sludge yield, biogas production and running cost, the traditional combined anaerobic-SBR process is unfeasible to treat swine wastewater, while the combined anaerobic-SBR process with addition of raw swine wastewater can be a suitable biotechnology.     

Denitrification of wastewater containing high nitrate and calcium concentrations

The removal of nitrate from rinse wastewater generated in the stainless steel manufacturing process by denitrification in a sequential batch reactor (SBR) was studied. Two different inocula from wastewater treatment plants were tested. The use of an inoculum previously acclimated to high nitrate concentrations led to complete denitrification in 6h (denitrification rate: 22.8mg NO(3)(-)-N/gVSSh), using methanol as carbon source for a COD/N ratio of 4 and for a content of calcium in the wastewater of 150mg/L. Higher calcium concentrations led to a decrease in the biomass growth rate and in the denitrification rate. The optimum COD/N ratio was found to be 3.4, achieving 98% nitrate removal in 7h at a maximum rate of 30.4mg NO(3)(-)-N/gVSSh and very low residual COD in the effluent.     

Integration of a Coagulation/Flocculation step in a biological sequencing batch reactor for COD and nitrogen removal of supernatant of anaerobically digested piggery wastewater

The supernatant from mesophilic anaerobic digestion of piggery wastewater is characterised by a high amount of COD (4.1 g COD L(-1)), ammonium (2.3g NH(4)(+)-NL(-1)) and suspended solids (2.5 g SS L(-1)). This effluent can be efficiently treated by means of a Sequencing Batch Reactor (SBR) strategy for biological COD, SS and nitrogen removal including a Coagulation/Flocculation step. Total COD and SS reduction yields higher than 66% and 74%, respectively, and a total nitrogen removal (via nitrite) of more than 98% were reached when working with HRT 2.7 days, SRT 12 days, temperature 32 degrees C, three aerobic/anoxic periods, without external control of pH and under limited aeration flow. The inhibition of nitrite oxidizing biomass was achieved by the working free ammonia concentration and the restricted air supply (dissolved oxygen concentration below 1 mg O(2)L(-1)). Since a part of the total COD was colloidal and/or refractory, a Coagulation/Flocculation step was implemented inside the SBR operating strategy to meet a suitable effluent quality to be discharged. Several Jar-Tests demonstrated that the optimal concentration of FeCl(3) was 800 mg L(-1). A respirometric assay showed that this coagulant dosage did not affect the biological activity of nitrifying/denitrifying biomass.     

Aerobic granulation with brewery wastewater in a sequencing batch reactor

Aerobic granular sludge was cultivated in a sequencing batch reactor fed with brewery wastewater. After nine-week operation, stable granules with sizes of 2-7 mm were obtained. With the granulation, the SVI value decreased from 87.5 to 32 mL/g. The granular sludge had an excellent settling ability with the settling velocity over 91 m/h. Aerobic granular sludge exhibited good performance in the organics and nitrogen removal from brewery wastewater. After granulation, high and stable removal efficiencies of 88.7% COD(t), 88.9% NH(4)(+)-N were achieved at the volumetric exchange ratio of 50% and cycle duration of 6h. The average COD(t) and COD(s) of the effluent were 212 and 134 mg/L, respectively, and the average effluent ammonium concentration was less than 14.4 mg/L. Nitrogen was removed due to nitrification and simultaneous denitrification in the inner core of granules.     

An Integrated System for the Bioremediation of Wastewater Containing Xenobiotics and Toxcic Metals

An integrated system for the biotreatment of acidic wastewaters containing both toxic metals and organics is presented. It consists of two bioprocess stages (i) an anaerobic, SRB stage (containing alkaline‐tolerant s ulfate‐ r educing b acteria) that at pH 8 (chosen to acclimatize the bacteria in the biomedium) produces high concentrations of total sulfide ions (more than 400 mg/L) which are added to the wastewater to precipitate the heavy metals out at pH 2 as metal sulfides, and (ii) an aerobic, acidophilic stage containing heterotrophic bacteria (WJB3) that degrade organic xenobiotics. The anaerobic system was comprised of a 4‐L fluidized bed bioreactor with immobilized SRB, a mixing tank, and a precipitation tank. The effluent from the bioreactor with a high concentration of sulfide ions was fed into a mixing tank where model wastewaters containing toxic metals and phenol at pH 2 were also fed at increasing loading rates until free metal ions could be detected in the precipitation tank outlet. Then the effluent from the precipitation tank outlet was fed into a 2.5‐L aerobic bioreactor in which phenol was degraded. In this research, 100 % removal efficiencies were obtained with wastewaters containing more than 400 mg/L metal ions and 900 mg/L phenol at a 6‐h HRT of the mixing tank.     

Treatment of tomato processing wastewater by an upflow anaerobic sludge blanket-anoxic-aerobic system

The main objective of this study is to assess the achievability of stringent discharge criteria i.e. BOD(5)<15 mg/L, TSS<15 mg/L and NH(4)-N<1mg/L during the treatment of tomato processing wastewater with COD of 2800-15,500 mg/L, BOD(5) of 1750-7950 mg/L, TKN of 48-340 mg/L and NH(4)-N of 21-235 mg/L. Two treatment systems, a UASB-aerobic system and a UASB-anoxic-aerobic system were tested. Furthermore due to alkalinity deficiency, in the raw wastewater, the study explored varying UASB effluent recirculation flowrates to the UASB influent to reduce additional alkalinity requirements. The UASB-anoxic-aerobic system was effective in treating tomato canning wastewater at an overall HRT of 1.75 days while achieving 98.5% BOD(5), 95.6% COD, 84% TSS and 99.5% NH(4)-N removal producing effluent BOD(5), COD, TSS, NH(4)-N, TKN, NO(2)-N, NO(3)-N and PO(4)-P of 10, 70, 15, 0.5, 3, 0, 60 and 4 mg/L, respectively. The biogas yield was 0.43 m(3)/kg COD removed.     

Nutrient recovery from domestic wastewater using a UASB-duckweed ponds system

The pilot-scale wastewater treatment system used in this study comprised a 40-l UASB reactor (6-h HRT) followed by three duckweed ponds in series (total HRT 15 days). During the warm season, the treatment system achieved removal values of 93%, 96% and 91% for COD, BOD and TSS, respectively. Residual values of ammonia, TKN and total phosphorus were 0.41 mg N/l, 4.4 mg N/l and 1.11 mg P/l, with removal efficiencies of 98%, 85% and 78%, respectively. The system achieved 99.998% faecal coliform removal during the warm season with final effluent containing 4 x 10(3) cfu/100 ml. During the winter, the system was efficient in removing COD, BOD and TSS but not nutrients. The system was deficient in the removal of faecal coliforms during the winter, producing effluent with 4.7 x 10(5) cfu/100 ml. During the warm season, the N removal consisted of 80% by plant uptake, 5% by sedimentation and 15% unaccounted for. A duckweed production rate of 33 t dry matter per hectare per 8 months was achieved.     

Performance evaluation and phylogenic analysis of a full-scale subsurface cobble-bed biofilm system

The purpose of this study is to evaluate the efficiency of municipal wastewater treatment by a subsurface cobble-bed biofilm system (SCBS) in Taipei, Taiwan. In contrast to traditional wastewater treatment facilities, SCBS uses cobbles as the contact media in the biofilm treatment unit. In this study, the SCBS consists of a series of underground treatment units, including a sedimentation tank, a grit chamber, two bar screens, a pumping station, a distribution tank, a collection tank and an effluent tank. At the flowrate of 4000 m³/day, the average influent concentrations for biochemical oxygen demand, suspended solid, ammonium nitrogen, and total phosphorus were 66.99 mg/L, 26.14 mg/L, 17.33 mg/L, and 1.96 mg/L, respectively. After 39 months of operation, the measured influent and effluent results show that the treatment efficiencies obtained from the SCBS for biochemical oxygen demand, suspended solid, ammonium nitrogen, and total phosphorus are 91.3%, 84.0%, 84.0%, and 26.0%, respectively. The result of a first-order kinetic analysis shows that the NH₃-N degradation constant is greater than the BOD degradation constant in this cobble-bed biofilm unit. Probability analysis revealed that the SCBS may be an attractive alternative from the perspectives of treatment efficiency for municipal wastewater treatment. Klebsiella spp. were found to be the predominant species in the biofilm system in the SCBS.     

实验室模拟高负荷SPAC厌氧反应器运行

采用模拟废水, 对新型高负荷螺旋式自循环(Spiral automatic circulation, SPAC)厌氧反应器的运行性能进行了实验室模拟研究。结果表明: 在30oC, 水力停留时间(HRT)为12 h, 进水COD浓度从8000 mg/L升至20 000 mg/L的条件下, 反应器的COD去除率为91.1%~95.7%, 平均去除率为93.6％。在进水浓度为20 000 mg/L, HRT由5.95 h缩短至1.57 h的工况下, COD去除率从96.0%降低至78.7%, 反应器达到最高容积负荷率306 g COD/(L·d), 最大容积COD去除率240 g/(L·d), 最高容积产气率131 L/(L·d)。该反应器对基质浓度的连续提升具有良好的适应能力。进水COD浓度由8000 mg/L提升至20 000 mg/L时, 出水COD浓度一直处在较低水平(平均为852?mg/L), 容积COD去除率和容积产气率分别提高162%和119%。该反应器对HRT的连续缩短也有良好的适应能力。HRT由5.95 h缩短至1.57 h时,反应器容积COD去除率和容积产气率分别升高191%和195%。     

Photosynthetic based algal-bacterial combined treatment of mixtures of organic pollutants and CO2 mitigation in a continuous photobioreactor

An algal-bacterial microcosm was synthetically constructed of Chlorella vulgaris MMl and Pseudomonas MTl. This microcosm was able to treat simulated wastewater supplemented with mixtures of phenol and pyridine up to 4.6 and 4.4 mM, respectively, in a continuous stirred tank bioreactor (CSTR) using photosynthetic oxygenation. Complete pollutant removal and detoxification and 82 % removal of introduced chemical oxygen demand (COD) were achieved at a hydraulic retention time (HRT) of 2.7 days. Increasing the influent load to 5.3 and 6.3 mM reduced the removal of phenol, pyridine and COD to 78, 21 and 59 %, respectively. Fertilization of the photobioreactor with 24 mM NaHCO₃ restored the treatment and detoxification efficiencies. The system was able to additionally mitigate up to 72 mM NaHCO₃ at the same HRT. Although the fertilization increased the system treatment efficiency, the settleability of the algal-bacterial microcosm was significantly reduced. When the photobioreactor was operated at HRT of 2.7 days in a 12/12 h of dark/light cycle, complete removal of 4.7 mM phenol was recorded but only 11 % of 5.7 mM pyridine was removed. The COD removal efficiency and CO₂ mitigation were also reduced to 65 and 86 %, respectively, and the effluent retained significant toxicity where 73 % inhibition was recorded. Elongation of the illumination time to 48 h (HRT of 4 days at 12/12 h dark/light cycle) restored the treatment and detoxification efficiencies.     

Effect of COD/N ratio and salinity on the performance of sequencing batch reactors

The effects of COD/N ratio (3-6) and salt concentration (0.5-2%) on organics and nitrogen removal efficiencies in three bench top sequencing batch reactors (SBRs) with synthetic wastewater and one SBR with fish market wastewater were investigated under different operating schedules. The solids retention time (SRT, 20-100 days) and aeration time (4-10h) was also varied to monitor the performance. For synthetic wastewater, chemical oxygen demand (COD) removal efficiencies were consistently greater than 95%, irrespective of changes in COD/N ratio, aeration time and salt concentrations. Increasing the salt concentrations decreased the nitrification efficiency, while high COD/N ratio's favored better nitrogen removal (>90%). The treatment of real saline wastewater ( approximately 3.2%) from a fish market showed high COD (>80%) and nitrogen (>40%) removal efficiencies despite high loading rate and COD/N fluctuations, which is due to the acclimatization of the biomass within the SBR.