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.     

Improvement of fruit and vegetable waste anaerobic digestion performance and stability with co-substrates addition

The effect of fish waste (FW), abattoir wastewater (AW) and waste activated sludge (WAS) addition as co-substrates on the fruit and vegetable waste (FVW) anaerobic digestion performance was investigated under mesophilic conditions using four anaerobic sequencing batch reactors (ASBR) with the aim of finding the better co-substrate for the enhanced performance of co-digestion. The reactors were operated at an organic loading rate of 2.46–2.51 g volatile solids (VS) l⁻¹ d⁻¹, of which approximately 90% were from FVW, and a hydraulic retention time of 10 days. It was observed that AW and WAS additions with a ratio of 10% VS enhanced biogas yield by 51.5% and 43.8% and total volatile solids removal by 10% and 11.7%, respectively. However FW addition led to improvement of the process stability, as indicated by the low VFAs/Alkalinity ratio of 0.28, and permitted anaerobic digestion of FVW without chemical alkali addition. Despite a considerable decrease in the C/N ratio from 34.2 to 27.6, the addition of FW slightly improved the gas production yield (8.1%) compared to anaerobic digestion of FVW alone. A C/N ratio between 22 and 25 seemed to be better for anaerobic co-digestion of FVW with its co-substrates. The most significant factor for enhanced FVW digestion performance was the improved organic nitrogen content provided by the additional wastes. Consequently, the occurrence of an imbalance between the different groups of anaerobic bacteria which may take place in unstable anaerobic digestion of FVW could be prevented.     

Anaerobic digestion of agro-industrial waste enriched with bovine bone meal for improved biogas production and biofertilization

The increase in animal and agro-industrial production must be accompanied by the development of appropriate waste and by-product management strategies. Anaerobic digestion is a promising approach to recycle these wastes and reintegrate them into the economic production cycle of biogas and biofertilizer. In order to improve the performance of the anaerobic mesophilic digestion of abundant agro-industrial wastes constituted by potato peel (PP), and poultry waste (PW) and study the contribution of bovine bone meal (BB) as additive rich in phosphorus, which can help to neutralize the acidity of the substrate. The 10-point simplex-centroid design and the isoresponse surfaces strategy were used. This study demonstrated that in mesophilic bio-digestion, the using bovine bones in admixture with agroindustrial residue provided for the proper balance of chemical components required for proliferation of microbiological agent of bioconversion, which also resulted in an increase in biogas production capacity. The best formula was so composed by 66.67% bovine bone, 16.67% potatoes peel, and 16.67% poultry waste. The stability was achieved here after only 12 days. The digestate generated from it was fulfilled with the microbiological and chemical requirements for safety defined by the NF U44-551 standard. Germination test revealed that this optimal produced digestate, did not hinder growth, in fact, almost 85% of seed was germinated. Finally, fertilization experiments prove that this digestate can boost the growth of bell pepper (Capsicum annuum).     

Performance and stability of an anaerobic fixed bed reactor subjected to progressive increasing concentrations of influent organic matter and organic shock loads

Data on the performance of a horizontal-flow anaerobic immobilized biomass (HAIB) reactor subjected to step increases of organic loading rates (OLR) and to organic shock loads (OSL) are presented and discussed. The tubular reactor (100 cm long and 5 cm diameter) with a useful volume of 1995 mL was filled with polyurethane foam cubic matrices holding immobilized biomass and fed with synthetic wastewater. The reactor was operated at the controlled temperature of 30+/-1 degrees C and hydraulic retention time of 7 h. After about 15 days, the HAIB reactor attained operating stability. Thereafter, it was subjected to step increases of the applied OLR that ranged from 6.8 to 18.8 kg COD/m(3)d. After steady state had been achieved at each step, OSL corresponding to approximately three times the operating OLR were applied for 7 h. No disturbance was observed due to the step increase in OLR. An increase in effluent chemical oxygen demand (COD) and volatile fatty acids (VFA) concentrations and a decrease in the percentage of methane in the biogas were observed due to OSL applications. However, stability of the monitoring parameters was always restored approximately 17 h after the application of OSL for all conditions tested.     

Estimation of Biogas Generation from a Uasb Reactor via Multiple Regression Model

In this study, regression analysis based an estimation model for biogas generated from an up-flow anaerobic sludge blanket (UASB) reactor treating landfill leachate is developed using several leachate parameters, such as pH, conductivity, total dissolved solids, chemical oxygen demand, alkalinity, chloride, total Kjeldahl nitrogen, ammonia, total phosphorus. These landfill leachate parameters are monitorized over a period of 1000 days at 35 ± 1°C in the UASB reactor. In order to develop the best model giving highest estimation performance, eight model equations including different input parameter combinations are analyzed. Based on the results of regression analysis, the best coefficients of the model equation are determined. As a conclusion, the developed model in this study can give accurate biogas amount prediction for the USAB reactor-based leachate treatment system.     

中温厌氧消化垃圾焚烧发电厂渗滤液的试验研究

采用逐渐提高有机负荷的半连续进料方式,研究中温(35℃左右)条件下,猪粪为接种物,厌氧消化焚烧发电厂垃圾渗滤液的消化规律。试验以5%为单位,由5%体积负荷渗滤液起开始填料,逐步提高至35%的体积负荷。试验进行的7个负荷,消化系统pH值稳定在7.2~7.8之间,碱度、氨氮浓度较高,分别在7803~17948 mg/L、673~1630 mg/L之间,为系统提供了良好的酸碱缓冲环境。低负荷时,VFA值较低,生物气中甲烷含量稳定在60%左右;高负荷时,随着渗滤液的加入,VFA值波动较大,甲烷含量也随VFA值的变化起伏波动(25%负荷时,甲烷含量出现峰值,高达75.5%)。消化系统共进料2800 mL渗滤液(即197.3 gCODCr),累计产气量83086 mL,平均每gCODCr产沼气约421.1 mL(平均gCODcr产甲烷约273.7 mL)。进水渗滤液CODCr浓度为70472 mg/L,实验结束时,消化液CODCr浓度降至3373 mg/L,CODCr去除率高达95.2%。     

The maturity tests during the composting of municipal solid wastes

This study investigated at first the evolution of co-composting process of municipal solid waste and sewage sludge under Tunisian pedo-climatic conditions.Results showed that the temperature profiles established in the system revealed three classical steps, the mesophilic phase during the first 25 days, the thermophilic phase between 30 and 130 days and the cooling phase began after the 14th week in the two windrows W1 (100% of municipal solid wastes) and W2 (60% of municipal solid wastes and 40% of dried sewage sludge). Potential toxic heavy metal content appeared generally more important in W2 than W1, and both finished products of compost obtained in this study satisfied most parts of the recommended norms of agronomical use. The presence or absence of nitrifying activity allowed determining that the compost W1 was more mature than the compost W2.Composting cannot only transform waste by reducing its harmful effect but also corrects when added to soil, the deficit in organic matter. The nature of the raw material used in composting may affect the quality of the final product. There is a significant need for the amendment of soils by compost. The quality of the amendment may have a significant impact on environment.     

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.     

An overview on biogas generation from anaerobic digestion of food waste

Food waste is an inevitable type of waste in every city, and its treatment technology evolves with time. Due to the high organic content and high biodegradability of food waste, anaerobic digestion becomes a commonly accepted treatment method to deal with it. This review article summarizes key factors for anaerobic digestion and provides useful information for successful anaerobic digestions. Reasonable temperature and pH are essential for a successful and productive anaerobic digestion process. A good inoculum to substrate ratio triggers a profitable food waste digestion. Good mixing and small particle sizes are important factors too. In addition, the pros and cons of different reactors to food waste digestion are highlighted. Moreover, co-digestion of food waste with animal manures, sewage sludge, and green waste were introduced.     

厌氧氨氧化工艺处理猪场废水沼液的试验研究

本文以实际猪场沼气废水为研究对象,以ASBR为反应器,接种厌氧消化污泥培养厌氧氨氧化细菌,厌氧氨氧化阶段成功启动后,研究了厌氧氨氧化脱氮最佳运行工艺。试验研究表明,厌氧氨氧化反应适宜的温度在35（±1）℃之间,适宜的pH在7．5—8．0之间,HRT选用24h。当达到最佳运行参数时,NH4＋-N的去除率达到87．6％,NO2- -N的去除率达到99．96％。     

污泥高固体厌氧消化研究进展

厌氧消化是实现污泥的减量化、稳定化和资源化的重要手段,相对于传统的低浓度污泥厌氧消化工艺高固体污泥厌氧消化可以直接利用污水处理厂排放的脱水污泥,具有设施体积小、单位容积产气率较高和水耗及能耗较低等优势。本文综述了近年来污泥高固体消化的研究进展,从污泥高固体厌氧消化的基本特征出发,总结了污泥高固体厌氧消化的影响因素和对反应器的要求;同时对污泥高固体消化存在的搅拌不匀、传质传热困难、有机质降解率偏低、搅拌系统不成熟等问题作了简要分析,这些问题都还有待于深入研究解决。     

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.     

Evaluation of Biogas Yield of Selected Ratios of Cattle,Swine, and Poultry Wastes

Production of biogas from animal wastes could lessen the problems of energy shortage and indiscriminate animal waste disposal. A study of anaerobic digestion of selected ratios of cattle, swine, and poultry wastes was carried out to evaluate their biogas yields. Cattle (C), swine (S), and poultry (P) wastes were mixed as C:S:P in the following ratios: 1:0:0 (control), 1:0:1, 4:1:3, 2:1:1, 4:3:1, and 1:1:0 by mass to obtain six samples of of 0.4 kg each, referred to as samples 1 to 6 respectively. A quantity (0.1 kg) of inoculum (obtained by pre-fermenting equal masses of poultry waste and water for 50 days under anaerobic condition) and 0.5 kg of water were added to each of the samples. The resulting slurries were digested in triplicates for 30 days in 1.3 L laboratory-scale anaerobic digesters. The volume of biogas produced was obtained by downward displacement of water in a measuring cylinder. The cumulative biogas yields of samples 1 to 6 were 332.5, 497.5, 487.5, 467.5, 457.5, and 430.0 cm³/kg slurry respectively. The cumulative biogas yields of samples 2 and 3 were significantly (p < 0.05) higher than those of the other samples but not significantly (p > 0.05) different from each other. However, the cumulative biogas yield of sample 1 was significantly (p < 0.05) lower than those of the other samples. The study revealed that a blend of equal masses of cattle and poultry wastes is optimum for biogas production.     

Alternative treatment for septic tank sludge: co-digestion with municipal solid waste in bioreactor landfill simulators

Co-disposal of septic tank sludge had a positive effect on the municipal solid waste (MSW) stabilisation process in Bioreactor Landfill simulators. Co-disposal experiments were carried out using the Bioreactor Landfill approach aiming to solve the environmental problems caused by indiscriminate and inadequate disposal of MSW and especially of septic tank sludge. The simulator receiving septic tank sludge exhibited a 200 days shorter lag-phase as compared to the 350 days required by the control simulator to start the exponential biogas production. Additionally, the simulator with septic sludge apparently retained more moisture (>60% w/w), which enhanced the overall conversion of organic matter hence increasing the biogas production (0.60 m3 biogas kg(-1)VS(converted)) and removal efficiency of 60% for VS from the simulator. Alkaline pH values (pH>8.5) did not inhibit the biogas production; moreover it contributed to reduce partially the negative effects of NH(4)(+) (>2 g L(-1)) due to NH(3) volatilisation thus reducing the nitrogen content of the residues. Associated risks and hazards with septage disposal were practically eliminated as total coliform and faecal coliform contents were reduced by 99% and 100%, respectively at the end of the experiment. These results indicate that co-disposal has two direct benefits, including the safe and environmentally sound disposal of septic tank sludge and an improvement of the overall performance of the Bioreactor Landfill by increasing moisture retention and supplying a more acclimatised bacterial population.     

Biogas production from pistachio (Pistaciavera L.) de-hulling waste

Pistachio processing wastes create significant waste management problems unless properly managed. However, there are not well-established methods to manage the waste generated during the processing of pistachios. Anaerobic digestion can be an attractive option not only for the management of pistachio processing wastes but also producing renewable energy in the form of biogas. This study investigated anaerobic digestibility and biogas production potential of pistachio de-hulling waste from wet de-hulling process. Best to our knowledge, this is the first report on biogas production from pistachio de-hulling waste. The results indicated that (1) anaerobic digestion of pistachio de-hulling wastewater, solid waste, and their mixtures in different ratios is possible with varying levels of performance; (2) 1 L of de-hulling wastewater (chemical oxygen demand concentration of 30 g/L) produced 0.7 L of methane; (3) 1 L of de-hulling wastewater and 20 g of pistachio de-hulling solid waste produced 1.25 L of methane; and (4) 1 g of de-hulling solid waste produced 62.6 mL of methane (or 134 mL of biogas).     

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.     

Biohythane production from pineapple peel using Methanosarcina mazei enhanced with palm oil mill effluent (POME) sludge in single-stage anaerobic digestion

Biohythane production via single-stage anaerobic digestion (AD) is an effective way for sustainable energy recovery from lignocellulosic biomass. In this paper, biohythane was produced through the AD process from pineapple peel waste substrate using purely cultured Methanosarcina mazei with the enhancement of palm oil mill effluent (POME) sludge as the inoculum. This study focuses on the effects of the lignocellulosic pre-treatment method, the addition of POME sludge into M. mazei culture medium as inoculum, and various operational conditions (food to microorganisms (F/M) ratios, temperature, pH) on gas production performances. The experimental results indicate that these parameters influenced the efficiency of biohythane production by producing the peak maximum biohythane production rate values (HPR_max) and (MPR_max), H₂:CH₄ = 1.93:0.67 L/L-d, and biohythane yield (HY) and (MY), H₂:CH₄ = 1.18:0.55 mL/L-substrate. This study demonstrates that biohythane gas (H₂ + CH₄ + CO₂) production from pineapple waste can be accelerated by M. mazei only with the enhancement of POME sludge through single-stage AD system under mesophilic batch process conditions.     

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.     

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.     

市政污泥与高浓度废弃物的厌氧共消化：一种生物质能源净产生的途径

厌氧共消化是一种绿色、实用的回收废弃物中能源的技术。本文介绍了厌氧共消化技术的原理，并介绍了美国佐治亚州F. Wayne Hil水资源处理中心采用油脂废弃物（FOG）和含糖工业废水与市政污泥进行连续流厌氧共消化的实际应用案例。结果表明，厌氧共消化可显著提高甲烷产量达2倍以上，甲烷产量随着高浓度有机废弃物负荷率及厌氧消化反应器停留时间的延长而增加，且COD和VS降解率可保持在合理范围内，经济效益显著。