Anaerobic digestion and wastewater treatment systems

Upflow Anaerobic Sludge Bed (UASB) wastewater (pre-)treatment systems represent a proven sustainable technology for a wide range of very different industrial effluents, including those containing toxic/inhibitory compounds. The process is also feasible for treatment of domestic wastewater with temperatures as low as 14–16° C and likely even lower. Compared to conventional aerobic treatment systems the anaerobic treatment process merely offers advantages. This especially is true for the rate of start-up. The available insight in anaerobic sludge immobilization (i.e. granulation) and growth of granular anaerobic sludge in many respects suffices for practice. In anaerobic treatment the immobilization of balanced microbial communities is essential, because the concentration of intermediates then can be kept sufficiently low.So far ignored factors like the death and decay rate of organisms are of eminent importance for the quality of immobilized anaerobic sludge. Taking these factors into account, it can be shown that there does not exist any need for phase separation when treating non- or slightly acidified wastewaters. Phase separation even is detrimental in case the acidogenic organisms are not removed from the effluent of the acidogenic reactor, because they deteriorate the settleability of granular sludge and also negatively affect the formation and growth of granular sludge. The growing insight in the role of factors like nutrients and trace elements, the effect of metabolic intermediates and end products opens excellent prospects for process control, e.g. for the anaerobic treatment of wastewaters containing mainly methanol.Anaerobic wastewater treatment can also profitably be applied in the thermophilic and psychrophilic temperature range. Moreover, thermophilic anaerobic sludge can be used under mesophilic conditions.The Expanded Granular Sludge Bed (EGSB) system particularly offers big practical potentials, e.g. for very low strength wastewaters (COD 1 g/l) and at temperatures as low as 10° C. In EGSB-systems virtually all the retained sludge is employed, while compared to UASB-systems also a substantially bigger fraction of the immobilized organisms (inside the granules) participates in the process, because an extraordinary high substrate affinity prevails in these systems. It looks necessary to reconsider theories for mass transfer in immobilized anaerobic biomass.Instead of phasing the digestion process, staging of the anaerobic reactors should be applied. In this way mixing up of the sludge can be significantly reduced and a plug flow is promoted. A staged process will provide a higher treatment efficiency and a higher process stability. This especially applies for thermophilic systems.     

Performance of down-flow hanging sponge (DHS) reactor coupled with up-flow anaerobic sludge blanket (UASB) reactor for treatment of onion dehydration wastewater

In this study, a promising system consisting of up-flow anaerobic sludge blanket (UASB) reactor followed by down-flow hanging sponge (DHS) reactor was investigated for onion dehydration wastewater treatment. Laboratory experiments were conducted at two different phases, i.e., phase (1) at overall hydraulic retention time (HRT) of 11 h (UASB reactor: 6 h and DHS reactor: 5 h) and phase (2) at overall HRT of 9.4 h (UASB reactor: 5.2 h and DHS reactor: 4.2 h). Long-term operation results of the proposed system showed that its overall TCOD, TBOD, TSS, TKN and NH₄N removal efficiencies were 92 ± 5, 95 ± 2, 95 ± 2, 72 ± 6 and 99 ± 1.3%, respectively (phase 1). Corresponding values for the 2nd phase were 85.4 ± 5, 86 ± 3, 87 ± 6, 65 ± 8 and 95 ± 2.8%. Based on the available results, the proposed system could be more viable option for treatment of wastewater generated from onion dehydration industry in regions with tropical or sub-tropical climates and with stringent discharge standards.     

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.     

Treatment of slaughterhouse wastewater in a UASB reactor and an anaerobic filter

A study was performed to assess the feasibility of anaerobic treatment of slaughterhouse wastewaters in a UASB (Upflow Anaerobic Sludge Blanket) reactor and in an AF (Anaerobic Filter). Among the different streams generated, the slaughter line showed the highest organic content with an average COD of 8000 mg/l, of which 70% was proteins. The suspended solids content represented between 15 and 30% of the COD. Both reactors had a working volume of 21. They were operated at 37°C. The UASB reactor was run at OLR (Organic Loading Rates) of 1–6.5 kg COD/m³/day. The COD removal was 90% for OLR up to 5 kg COD/m³/day and 60% for an OLR of 6.5 kg COD/m³/day. For similar organic loading rates, the AF showed lower removal efficiencies and lower percentages of methanization. At higher OLR sludge, flotation occurred and consequently the active biomass was washed out from the filter. The results indicated that anaerobic treatment systems are applicable to slaughterhouse wastewaters and that the UASB reactor shows a better performance, giving higher COD removal efficiencies than the AF.     

Study of microbial community structures in UASB sludge treating municipal wastewater by denaturing gradient gel electrophoresis of 16S rDNA

The structures of microbial communities in lab-scale upflow anaerobic sludge blanket (UASB) reactors for treating municipal wastewater with different ratios of COD soluble/ COD total were studied using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes. The microbial structure of the inoculum sludge obtained from a full-scale UASB reactor of treating potato processing wastewater was compared with the structures of sludges collected from three lab-scale UASB reactors after eight months feeding with raw municipal wastewater, with CEPS (chemically enhanced primary sedimentation) pretreated municipal wastewater, and with a synthetic municipal sewage, respectively. Computer-aided numerical analysis of the DGGE fingerprints showed that the bacterial community underwent major changes. The sludges for treating raw and CEPS pretreated wastewater had very similar bacterial and archaeal communities (82% and 96% similarity) but were different from that for treating the synthetic sewage. Hence, despite     

Effect of temperature on low-strength wastewater treatment by UASB reactor using poly(vinyl alcohol)-gel carrier

The feasibility of treating low-strength wastewater with an up-flow anaerobic sludge blanket (UASB) reactor, using a poly(vinyl alcohol)-gel carrier, at various temperatures and hydraulic retention times (HRTs) was examined. The temperature was decreased from 35°C to 25°C and then to 15°C. The HRT was reduced from 2.0 h to 0.22 h. The COD removal rate reached 28 kg-COD m(-3)d(-1) at 35°C, 16 kg-COD m(-3)d(-1) at 25°C, and 6 kg-COD m(-3)d(-1) at 15°C. The COD removal rate was reduced by half for each temperature reduction of 10°C.     

上流式厌氧污泥床处理废液及其有关剖析

国内用上流式厌氧污泥床（ＵＡＳＢ）常温处理酵母废液的试验为数不多,本工作旨在启动ＵＡＳＢ装置中培育颗粒污泥,从而提高水处理程度。文中阐述了实验过程,且通过电镜考察污泥的微生物相,发现其间出现的“准颗粒污泥态”,同时还分析了工艺中产生的一种物质的“抑制临界状况”,推测对”完全的颗粒污泥态”的形成造成了阻遏。文中同时分析了发现的其它现象,对探索酵母废液ＵＡＳＢ常温处理深度的进一步提高有所裨益。     

The effect of pretreatment on anaerobic activity of olive mill wastewater using batch and continuous systems

This study was focused on several physico-chemical and biological treatment methods that may affect the reduction of the organic load in olive mill wastewater (OMW). In this study, removal of 95% of the phenolic compounds present in OMW was achieved using sand filtration and subsequent treatment with powdered activated carbon in a batch system. This pretreatment for OMW was found to enhance the anaerobic activity of the sludge in the batch system significantly. The efficiency of organic load removal achieved by the anaerobic treatment of untreated OMW in batch reactors with tap water dilution factors below 1:10, reached approximately 65% chemical oxygen demand (COD) removal. However, in the up-flow sludge anaerobic blanket (UASB) reactor, COD removal efficiency of 80–85% was reached at a hydraulic retention time (HRT) of 5 days with an influent COD concentration of 40 g l⁻¹ and organic loading rate (OLR)=8 g⁻¹ COD l⁻¹ per day.     

Enzymatic pre-hydrolysis and anaerobic degradation of wastewaters with high fat contents

Dairy wastewaters containing elevated fat and grease levels (868 mg l^–1) were treated in an upflow anaerobic sludge blanket reactor (UASB) and resulted in effluents of high turbidity (757 nephelometric turbidity units), volatile suspended solids up to 944 mg l^–1 and COD removal below 50%. When the same dairy wastewater was pre-treated with 0.1% (w/v) of fermented babassu cake containing Penicillium restrictum lipases, turbidity and volatile suspended solids were decreased by 75% and 90%, respectively, and COD removal was as high as 90%.     

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.     

Study of microbial community structures in UASB sludge treating municipal wastewater by denaturing gradient gel electrophoresis of 16S rDNA

The structures of microbial communities in lab-scale upflow anaerobic sludge blanket (UASB) reactors for treating municipal wastewater with different ratios of COD soluble/COD total were studied using denaturing gradient gel electrophoresis (DGGE) of 16S rRNA genes.The microbial structure of the inoculum sludge obtained from a full-scale UASB reactor of treating potato processing wastewater was compared with the structures of sludges collected from three lab-scale UASB reactors after eight months feeding with raw municipal wastewater, with CEPS (chemically enhanced primary sedimentation) pretreated municipal wastewater, and with a synthetic municipal sewage, respectively. Computer-aided numerical analysis of the DGGE fingerprints showed that the bacterial community underwent major changes. The sludges for treating raw and CEPS pretreated wastewater had very similar bacterial and archaeal communities (82%and 96% similarity) but were different from that for treating the synthetic sewage. Hence, despite similar % COD in the particulate form in the synthetic and the real wastewater, the two wastewaters were selected for different microbial communities. Prominent DGGE bands of Bacteria and Archaea were purified and sequenced. The 16S rRNA gene sequences of the dominant archaeal bands found in the inoculum, and UASB sludge fed with raw sewage, CEPS pretreated wastewater, and synthetic sewage were closely associated with Methanosaeta concilii. In the UASB sludge fed with synthetic sewage, another dominant band associated with an uncultured archaeon 39-2 was found together with M. concilii.     

Color removal of real textile wastewater by sequential anaerobic and aerobic reactors

Textile wastewater from the Pusan Dyeing Industrial Complex (PDIC) was treated utilizing a two-stage continuous system, composed of an upflow anaerobic sludge blanket reactor and an activated sludge reactor. The effects of color and organic loading rates were studied by varying the hydraulic retention time and influent glucose concentration. The maximum color load to satisfy the legal discharge limit of color intensity in Korea (400 ADMI, unit of the American Dye Manufacturers Institute) was estimated to be 2,700 ADMI·L⁻¹ day⁻¹. This study indicates that the two-stage anaerobic/aerobic reaction system is potentially useful in the treatment of textile wastewater.     

Post-Treatment Options for the Anaerobic Treatment of Domestic Wastewater

This paper focuses on the post-treatment options for the anaerobic treatment of domestic wastewater. Initially, the main limitations of anaerobic systems regarding carbon, nutrients and pathogen removal are presented. In sequence, the advantages of combined anaerobic/aerobic treatment and the main post-treatment options currently in use are discussed, including the presentation of flowsheets and a comparison between various post-treatment systems. Lastly, the paper presents a review of emerging options and possible improvements of current post-treatment alternatives.     

UASB-化学混凝技术处理草浆造纸废水的研究

采用UASB-化学混凝技术组合对草浆造纸废水进行处理。结果表明,接种颗粒污泥的二级启动,大大缩短了反应器的启动时间。在水力停留时间(HRT)6 h,进水COD逐渐提高的情况下对颗粒污泥进行驯化,20 d后pH、COD去除率趋于稳定。另外,通过L9(34)正交试验,研究了混凝中4因子影响大小的排序,并在最优条件下对UASB反应器出水进行混凝处理。组合技术处理的出水水质指标符合国家造纸工业污水排放标准。     

Evaluation of performance and microbial community in a two-stage UASB reactor pretreating acrylic fiber manufacturing wastewater

A two-stage UASB reactor was employed to pretreat acrylic fiber manufacturing wastewater. Mesophilic operation (35 ± 0.5 °C) was performed with hydraulic retention time (HRT) varied between 28 and 40 h. Mixed liquor suspended solids (MLSS) in the reactor was maintained about 8000 mg/L. The results showed COD and sulfate removal could be kept at 51% and 75%, respectively, when the HRT was no less than 38 h. Sulfate reduction mainly occurred in the acidification-stage reactor while methane production mainly occurred in the methane-stage reactor. The size of granule formed in the acidification-stage reactor ranged between 1 and 5 mm while the largest size of granule in the methane-stage reactor ranged from 0.5 to 2 mm. Compared to microbial populations in the acidification-stage reactor, the microbial diversity in methane-stage reactor was more abundant. In the acidification-stage reactor, the Syntrophobacter sulfatireducens devoted to both sulfate reduction and acetate production.     

人工神经网络的局域性对网络训练速度的影响

从网络结构入手,提出了网络局域性的概念。作为网络结构的一种定量描述,探讨了网络结构与训练速度、预测精度间的对应关系。结果表明网络的训练速度随局域性的增加而增加,网络的预测精神在局域性０．５５附近达到最高,任何偏离都会导致网络预测精度的下降。为在生化过程具体应用中选择合理的神经网络类型提供了理论依据。