Methanogenic toxicity and continuous anaerobic treatment of wood processing effluents

Wood processing effluents contain different types of phenolic compounds, from simple monomers to high molecular weight (MW) polyphenolic polymers, that can inhibit wastewater treatment. This work presents a comparative study of the methanogenic toxicity produced by three wood processing effluents (hardboard, fiberboard and BKME (kraft mill effluent)) using Pinus radiata, Eucalyptus and Tepa as feedstock (the last one being a native Chilean tree species). This study evaluates the influence of non-adapted granular and adapted flocculent sludge on forest industrial wastewater treatment as well as continuous anaerobic biodegradation of hardboard processing effluent using the upflow anaerobic sludge blanket (UASB). The adapted biomass (flocculent sludge) did not show any lag-phase signs. The 50% IC (the concentration causing 50% inhibition of methanogenic activity) was 4.3 g COD-effluent (chemical oxygen demand (COD)-of the effluent)/l and 2.8 g COD-effluent/l for the flocculent sludge and the granular sludge, respectively. The UASB system worked at low organic load rates (0.1-0.4 g COD/l d) with the COD removal ranging between 10 and 30%, and color removal did not occur under anaerobic conditions due to high MW. Indeed, the MW analysis indicates the presence of phenolic compounds over 25,000 Da in the anaerobic effluent.     

Treatment and reuse of sewage sludge

Sewage sludge was treated using composting, fixed-bed and stirred anaerobic digesters. The treatment performance in terms of the physico chemical parameters, bacterial indicators and pathogenic forms were assessed. In addition, the biogas production rate was recorded in the case of anaerobic digesters. Composting of the sewage sludge increased its total solids from 39 to 93% after 6 weeks, while the reduction in organic matter was 40% and the total nitrogen and phosphorus contents increased by 22 and 30%, respectively. Complete removal of salmonellae and faecal coliforms occurred, so that the composted sludge could be used as a soil conditioner and fertilizer. The results of the anaerobic treatment indicated that an organic load of 4.8kg COD m–3 per day achieved the best operating conditions for either the stirred or fixed-bed digester. The mean percentage removals of COD, BOD, faecal coliforms, faecal streptococci and the biogas production rate for the stirred digester were 53, 53, 24 and 29% and 259 L kg–1 COD per day, respectively. The corresponding mean percentage removals and production rate for the experiments with a fixed-bed digester were 61, 62, 33 and 35% and 328 L kg–1 COD per day, respectively. Improvements in the BOD and faecal coliform reductions and the gas production rate of 17, 38 and 21%, respectively, were achieved due to the presence of media (Berl saddles) in the fixed-bed digester. The microbial content of the anaerobically treated sludge is too high to be used as a fertilizer, while that of the composted sludge is low enough for such use.     

Performance of sequential anaerobic/aerobic digestion applied to municipal sewage sludge

A promising alternative to conventional single phase processing, the use of sequential anaerobic-aerobic digestion, was extensively investigated on municipal sewage sludge from a full scale wastewater treatment plant. The objective of the work was to evaluate sequential digestion performance by testing the characteristics of the digested sludge in terms of volatile solids (VS), Chemical Oxygen Demand (COD) and nitrogen reduction, biogas production, dewaterability and the content of proteins and polysaccharides. VS removal efficiencies of 32% in the anaerobic phase and 17% in the aerobic one were obtained, and similar COD removal efficiencies (29% anaerobic and 21% aerobic) were also observed. The aerobic stage was also efficient in nitrogen removal providing a decrease of the nitrogen content in the supernatant attributable to nitrification and simultaneous denitrification. Moreover, in the aerobic phase an additional marked removal of proteins and polysaccharides produced in the anaerobic phase was achieved. The sludge dewaterability was evaluated by determining the Optimal Polymer Dose (OPD) and the Capillary Suction Time (CST) and a significant positive effect due to the aerobic stage was observed. Biogas production was close to the upper limit of the range of values reported in the literature in spite of the low anaerobic sludge retention time of 15 days. From a preliminary analysis it was found that the energy demand of the aerobic phase was significantly lower than the recovered energy in the anaerobic phase and the associated additional cost was negligible in comparison to the saving derived from the reduced amount of sludge to be disposed.     

Relationships between anaerobic consortia and removal efficiencies in an UASB reactor degrading 2,4 dichlorophenol (DCP)

To gain more insight into the interactions between anaerobic bacteria and reactor performances (chemical oxygen demand-COD, 2,4 dichlorophenol-2,4 DCP removals, volatile fatty acid-VFA, and methane gas productions) and how they depended on operational conditions the microbial variations in the anaerobic granular sludge from an upflow anaerobic sludge blanket (UASB) reactor treating 2,4 DCP was studied. The study was composed of two parts. In the first part, the numbers of methanogens and acedogens in the anaerobic granular sludge were counted at different COD removal efficiencies. The relationships between the numbers of methanogens, the methane gas production and VFA production were investigated. The COD removal efficiencies increased to 74% from 30% while the number of total acedogens decreased to 10 from 30 cfu ml(-1). The number of total methanogens and acedogens varied between 11 x 10(3) and 10 x 10(9)MPN g(-1) and 10 and 30 cfu ml(-1) as the 2,4 DCP removal efficiencies were obtained between 60% and 99%, respectively. It was seen that, as the number of total acedogens decreased, the COD removal efficiencies increased. However, the number of total methanogens increased as the COD removal efficiencies increased. Correlations between the bacterial number and with the removal efficiencies obtained in different operational conditions were investigated. From the results presented in this paper a high correlation between the number of bacteria, COD removals, methane gas percentage, 2,4 DCP removals and VFA was observed. In the second part, methanogen bacteria in the anaerobic granular sludge were identified. Microbial observations and biochemical tests were applied to identify the anaerobic microorganisms from the anaerobic granular sludge. In the reactor treating 2,4 DCP, Methanobacterium bryantii, Methanobacterium formicicum, Methanobrevibacter smithii, Methanococcus voltae, Methanosarcina mazei, Methanosarcina acetivorans, Methanogenium bourgense and Methanospirillum hungatei were identified.     

Economic evaluation of sewage treatment processes in India

This paper evaluates the total annual cost including capital and operation and maintenance (O&M) costs for the up-flow anaerobic sludge blanket (UASB) and waste stabilization pond (WSP) systems operated in India. It also compares UASB and WSP systems with the activated sludge process (ASP) and biological aerated filter (BAF) systems in terms of total annual cost and chemical oxygen demand (COD) removal cost by assuming various annual interest rates and land prices. It was found that the relationship between capital and O&M costs per unit size of a UASB or WSP system and its treatment capacity can be established by a first-order equation. The relation between the cost of organic removal and capital or O&M cost for various sewage treatment systems at various annual interest rates revealed that, for the Indian context, UASB could be the most suitable option in terms of expenses and treatment efficiency.     

预处理方法对剩余活性污泥水解影响的比较研究

污泥预处理对污泥水解有较大促进作用,可以明显改善污泥的脱水、厌氧消化性能及其减量化。本文通过比较4种预处理方法加热、加碱、微波、超声波对剩余活性污泥水解性能的影响,探索效率高、成本低的污泥预处理技术。研究结果显示,加热、加碱对污泥水解的促进作用要明显高于微波、超声波预处理,其中加碱预处理的水解效率最高,处理后污泥的SCOD浓度最大提高了16.8倍,而SS、VSS最多分别减少了34%和41%。     

Biological treatment of anaerobically digested palm oil mill effluent (POME) using a Lab-Scale Sequencing Batch Reactor (SBR)

The production of highly polluting palm oil mill effluent (POME) has resulted in serious environmental hazards. While anaerobic digestion is widely accepted as an effective method for the treatment of POME, anaerobic treatment of POME alone has difficulty meeting discharge limits due to the high organic strength of POME. Hence, subsequent post-treatment following aerobic treatment is vital to meet the discharge limits. The objective of the present study is to investigate the aerobic treatment of anaerobically digested POME by using a sequencing batch reactor (SBR). The SBR performance was assessed by measuring Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) removal as well as Sludge Volume Index (SVI). The operating pH and dissolved oxygen concentrations were found to be 8.25–9.14 and 1.5–6.4 mg/L, respectively, throughout the experiment. The experimental results demonstrate that MLVSS, OLR and sludge loading rate (SLR) play a significant role in the organic removal efficiency of SBR systems and therefore, further investigation on these parameters was conducted to attain optimum SBR performance. Maximum COD (95–96%), BOD (97–98%) and TSS (98–99%) removal efficiencies were achieved at optimum OLR, SLR and MLVSS concentration ranges of 1.8–4.2 kg COD/m³ day, 2.5–4.6 kg TSS/m³ day and 22,000–25,000 mg/L, respectively. The effluent quality remained stable and complied with the discharge limit. At the same time, the sludge showed good settling properties with average SVI of 65. It is envisaged that the SBR process could complement the anaerobic treatment to produce final treated effluent which meets the discharge limit.     

酸性条件下厌氧颗粒污泥活性抑制与恢复试验研究

取食品生产废水处理中试工程运行中现有的厌氧颗粒污泥进行活性抑制与恢复试验。通过慢性致毒与急性致毒作用的对比,分析酸性条件对颗粒污泥的抑制作用,研究颗粒污泥的耐酸性,并考察污泥活性恢复方法。结果表明:当进水pH=6.5,颗粒污泥活性受到轻微抑制,不影响系统的稳定运行;当pH值下降至4.5时,COD去除率和产甲烷量均趋于零。同时使用调节进水pH值、降低进水有机负荷、提高进水碱度以及调整水力停留时间等4种方法能有效恢复污泥活性,活性达到抑制前的80%左右。     

Anaerobic-aerobic treatment of purified terephthalic acid (PTA) effluent; a techno-economic alternative to two-stage aerobic process

This paper addresses the treatment of purified terephthalic acid (PTA) effluent using anaerobic and aerobic processes. Laboratory studies were carried out on flow proportionate composite wastewater generated from the manufacturing of PTA. An activated sludge process (ASP-two stage and single stage) and an upflow anaerobic fixed film fixed bed reactor (AFFFBR) were used, individually and in combination. The performance of a full-scale ETP under existing operating conditions was also studied. Full scale ETP studies revealed that the treatment of PTA effluent using a two-stage ASP alone does not meet treated effluent quality within the prescribed Indian Standards. The biomass produced in the two stage ASP was very viscous and fluffy and the sludge volume index (SVI) was very high (200-450 ml/g). However, pretreatment of PTA effluent using an upflow AFFFBR ensured substantial reduction in BOD (63%) and COD (62%) with recovery of biogas at 1.8-1.96 l/l effluent treated at a volumetric loading rate (VLR) 4-5 kg COD/m(3) d. The methane content in the biogas varied between 55% and 60%. The pretreated effluent from the upflow AFFFBR was then treated through a single stage ASP. The biomass produced in the ASP after anaerobic treatment had very good settlability (SVI: 75-90 ml/g) as compared to the two stage ASP and the treated effluent quality with respect to BOD, COD and SS was within the prescribed Indian Standards. The alternative treatment process comprising an upflow AFFFBR and a single stage ASP ensured net power saving of 257 kW and in addition generated 442 kW of power through the AFFFBR.     

生物技术处理稠油废水的研究

试验分别利用三种生物处理方法：好氧、厌氧及酵母菌处理方法对稠油废水进行了处理。COD去除率在30%以下。在处理过程中,好氧污泥生物量表现出明显的增长。厌氧污泥及酵母菌在处理前后生物量几乎无变化。处理效果不明显与稠油废水可生化性差的性质有关,也与试验条件及选择菌种有关。     

Studies on the toxic effects of pentachlorophenol on the biological activity of anaerobic granular sludge

In order to explore the pathway of the anaerobic biotreatment of the wastewater containing pentachlorophenol (PCP) and ensure the normal operation of Upflow Anaerobic Sludge Blanket (UASB) reactor, the anaerobic sludge under different acclimation conditions were selected to seed and start up UASB reactors. Anaerobic toxicity assays were employed to study the biological activity, the tolerance and the capacity to degrade PCP of different anaerobic granular sludge from UASB reactors. Results showed that the anaerobic granular sludge acclimated to chlorophenols (CPs) could degrade PCP more quickly (up to 9.50mg-PCPg(-1)TVSd(-1)). And the anaerobic granular sludge without acclimation to CPs had only a little activity of degrading PCP (less than 0.07mg-PCPg(-1)TVSd(-1)). Different PCP concentrations (2, 4, 6, 8mgL(-1)) had different inhibition effects on glucose utilization, volatile fatted acidity (VFA)-degrading and methanogens activity of PCP degradation anaerobic granular sludge, and the biological activity declined with the increase in PCP concentration. The methanogens activity suffered inhibition from PCP more easily. The different acclimation patterns of seeded sludge had distinctly different effects on biological activity of the degradation of PCP of anaerobic granular sludge from UASB reactors. The biological activity of the anaerobic granular sludge acclimated to PCP only was also inhibited. This inhibition was weak compared to that of anaerobic granular sludge acclimated to CPs, further, the activity could recover more quickly in this case. In the same reactor, the anaerobic granular sludge from the mid and base layers showed higher tolerance to PCP than that from super layer or if the sludge is unacclimated to CPs, and the corresponding recovery time of the biological activity in the mid and base layers were short. Acetate-utilizing methanogens and syntrophic propinate degraders were sensitive to PCP, compared to syntrophic butyrate degraders.     

厌氧水解—高负荷生物滤池处理城镇污水的试验研究

厌氧水解－高负荷生物滤池是一种利用附着在塑料模块填料上的微生物系统对城镇污水中的污染物质进行降解处理的绿色环保技术。厌氧水解池和高负荷生物滤池采用的塑料模块填料具有高空隙率、高附着面积、高布水性能和抗堵塞的优异性能,并无须回流。当厌氧水解池水力停留时间为4小时,生物滤池水力负荷为30米^3/米^2。日,该系统处理城镇污水的CODCr去除率达80－86％,BOD5去除率达85％－95％。SS去除率达85－95％,处理后出水上述各项指标均可满足国家二级生物处理排放标准的要求。与广泛运用的活性法处理系统相比,该技术可节约基建投资20％以上,节约能耗50％以上,同时还具有流程简单、管理方便、耐冲击负荷、剩余污泥少等特点。     

Piggery waste treatment by anaerobic digestion and nutrient removal by ionic exchange

Piggery wastes must be treated before their disposal. The high solids content and high chemical oxygen demand of piggery wastes indicated that anaerobic biological treatment could be successfully applied as primary treatment. For that reason, a comparison between upflow anaerobic sludge bed reactor (UASB) and anaerobic fixed bed reactor (AFBR) at a similar organic volumetric loading rate of 5 kg DQO/m³ day was carried out. 60% of the piggery waste COD was removed with the AFBR compared to 40% with the UASB, thus showing a better performance of the AFBR. After 1-h sedimentation secondary process, both anaerobic effluents were treated by ionic exchange with natural zeolite due to their high values of ammoniacal nitrogen (NH⁺₄ plus free NH₃). The high removal of nutrients reported (90%) shows zeolite to be a good choice as tertiary treatment.     

Preliminary evaluation of the electrochemical and chemical coagulation processes in the post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor

The main objective of this paper was to perform a preliminary comparative study between chemical and electrochemical coagulation processes, both followed by flocculation and sedimentation of an effluent from an upflow anaerobic sludge blanket (UASB) reactor treating simulated wastewater from an unbleached Kraft pulp mill. The electrochemical treatment removed up to 67% (with aluminum electrodes) and 82% (with stainless-steel electrodes) of the remaining chemical oxygen demand (COD) and 84% (stainless steel) and 98% (aluminum) of the color in the wastewater. These efficiencies were achieved with an energy consumption ranging from 14 to 20 Wh l(-1). The coagulation-flocculation treatment with ferric chloride and aluminum sulfate removed up to 87% and 90% of COD and 94% and 98% of color, respectively. The addition of a high molecular weight cationic polymer enhanced both COD and color removal efficiencies. The two post-treatment processes proved to be technically feasible; however the economical feasibility could not be assessed since the experiments were performed with small reactors that could distort scale factors.     

柠檬酸废水处理改造工程实例

采用多级内循环厌氧反应器MIC/上升式厌氧反应器UASB串联工艺处理柠檬酸生产排放的高浓度有机废水,其中厌氧处理段的COD去除率＞94％,整体COD去除率可达98.3％左右.最终排放口出水COD平均值为190 mg/L,pH值为6～9,达到柠檬酸行业废水排放标准.     

Improving anaerobic sewage sludge digestion by implementation of a hyper-thermophilic prehydrolysis step

The present study focuses on a two-step process for treatment and stabilisation of primary sludge. The process consists of a hyper-thermophilic hydrolysis step operated at 70 degrees C and a hydraulic retention time (HRT) of 2 days followed by a thermophilic (55 degrees C) anaerobic digestion step at a HRT of 13 days. A one-step anaerobic digester operated at 55 degrees C and 15 days HRT was used as a reference process. The two-step process was characterized by a 12% higher organic suspended solids removal efficiency and better pathogen reduction effect than the conventional one-step digestion. The microbial community of the digester fed with pre-treated sludge was characterised by a higher activity compared to that of the digester treating raw sludge. Moreover, the pre-treatment of the primary sludge resulted up to 48% increase of the methane potential (20.09 and 13.56mmolCH(4)g(-)VS(-1) with and without pre-treatment, respectively) and up to 115% increase of the methane production rate. Finally it was shown that the extra energy requirements for the operation of a pre-treatment step would be covered by the energy produced from the extra methane production and in addition there would be a significant energy surplus of 2.17kJd(-1) for the system tested.     

超声处理对污泥厌氧消化的影响——消化效率对比

为研究超声处理对污泥消化效率的影响,笔者在大坦沙污水处理厂做了现场对比试验。所用的污泥分别为经过和未经过超声处理的污泥。试验结果显示,超声处理可以显著缩短消化罐的调试周期并提高消化效率,不同的混合比例可以使产气率提高30％～60％。     

Biological treatment of synthetic wastewater containing 2,4 dichlorophenol (DCP) in an activated sludge unit

Chlorophenol compounds present in many chemical industry wastewaters are resistant to biological degradation because of the toxic effects of such compounds on microorganisms. Synthetic wastewater containing different concentrations of 2,4 dichlorophenol (DCP) was subjected to biological treatment in an activated sludge unit. Effects of feed DCP concentration on COD, DCP, and toxicity removals and on sludge volume index were investigated at a constant sludge age of 10 days and hydraulic residence time (HRT) of 25 h. The Resazurin method based on dehydrogenase activity was used for assessment of toxicity for the feed and effluent wastewater. Percent COD, DCP, and toxicity removals decreased and the effluent COD, DCP, and toxicity levels increased with increasing feed DCP concentrations above 150 mgl(-1) because of inhibitory effects of DCP. Biomass concentration in the aeration tank decreased and the sludge volume index (SVI) increased with feed DCP concentrations above 150 mgl(-1) resulting in lower COD and DCP removal rates. The system should be operated at feed DCP concentrations of less than 150 mgl(-1) in order to obtain high COD, DCP, and toxicity removals.     

超声-生化法降解8-羟基喹啉废水的实验研究

本文采用超声-生化(两级好氧)联用的方法,对8-羟基喹啉废水的降解工艺进行了研究。对废水的预处理方法为超声降解法,文中分析了溶液初始浓度、超声时间、超声全程时间以及超声细胞粉碎机的变幅杆直径大小对废水预处理效果的影响。实验结果表明,变幅杆直径为25mm,溶液初始浓度为0.6g/L,超声全程时间在20min,最佳超声时间为2s时降解效率最高,CODcr去除率可以达到40.4%。本实验生化处理方法为普通活性污泥法(两级好氧),一级好氧反应池停留时间选择10h,去除率为69.4%;二级好氧反应池停留时间选择6h,去除率为71.7%。超声-生化(两级好氧)联用对8-羟基喹啉废水处理效果良好,CODcr总去除率达到94.4%。     

An experimental study on the influence of zeolite on changes of pH and alkalinity in anaerobic treatment of compost leachate

With the increase of urbanization, municipal solid waste has also increased. Therefore, the need for solid waste management is also increasing compared with earlier decades. Composting is a good option for the recycling of solid waste; however, it produces leachate, which requires proper treatment systems to prevent environmental degradation. Due to high chemical oxygen demand (COD) concentrations in compost leachate, anaerobic treatment is the best option for handling the effluent, and an anaerobic baffled reactor (ABR) is one such anaerobic reactor that can be used for its treatment. Because of high ammonia and heavy metal concentrations, as well as the possibility of sludge washout in ABRs, it is important to use proper media, such as zeolite, which can reduce inhibition effects and sludge washout from the reactor. Anaerobic treatment, especially during the methanogenesis phase, is sensitive, and pH and alkalinity are parameters that influence the treatment. Therefore, adjusting these parameters within a normal range is very important to the proper functioning of anaerobic systems. In this study, a pilot‐scale ABR was used, and the last 4 of the 8 ABR compartments were filled with zeolite. The bioreactor was operated at hydraulic retention times (HRT) of 3, 4, and 5 days, with zeolite filling ratios of 10%, 20%, and 30%, and influent COD concentrations of 10,000, 20,000, and 30,000 milligrams per liter (mg/L). In this study, pH value was 6.43 ± 0.1, 6.96 ± 0.3, and 6.96 ± 0.25 at filling ratios of 10%, 20%, and 30%, respectively. According to the results, in all filling ratios, no significant changes were observed in the pH value when the organic loading rate increased and its amount was within a constant range. Influent alkalinity was equal to 2015 ± 510, 2884 ± 505, and 4154 ± 233 milligrams of calcium carbonate per liter (mg CaCO₃/L) at influent COD concentrations of 10,000, 20,000, and 30,000 mg/L, respectively, and in effluent, they were 2536 ± 336, 3379 ± 639, and 4377 ± 325 mg CaCO₃/L, respectively. The amount of alkalinity in the effluent increased compared with the alkalinity in the influent. The results show that the amount of alkalinity in the influent and effluent was similar, and the alkalinity enhancement was lower when the filling ratio was increased from 10% to 20%, and 20% to 30%. Comparisons of the results from zeolite with and without biofilm showed that, in cases of zeolite with biofilm, the amounts of silica and oxygen decreased and the amount of carbon increased, and it showed the formation of biofilm on the surface of zeolite. In addition, the absence of sodium in the zeolite with the biofilm indicated that sodium was exchanged with ammonium ions. According to the results, zeolite can be used in anaerobic reactors as a medium, and it also reduces fluctuations in pH and alkalinity at different organic loading rates, providing a normal range for anaerobic treatment.