Combined adsorption and Chemical precipitation process for pretreatment or post-treatment of landfill leachate

Performances of combined adsorption and chemical precipitation were evaluated as one of the options for pretreatment or post-treatment of a municipal solid waste (MSW) landfill leachate and leachate from an industrial solid waste landfill. The COD and color removals of the leachate from a MSW landfill were 35% and 33% at an alum dose of 300 mg/L with preceding PAC (powdered activated carbon) dose of 200 mg/L, respectively. For MSW leachate, the combined adsorption and coagulation process showed 2.3 times higher COD removal at PAC dose of 200 mg/L and alum dose of 500 mg/L than the unit process of adsorption with poor settleability. The COD removal was accomplished mainly by adsorption, while coagulation was a key mechanism of color removal. The COD and color of the biologically treated leachate from an industrial solid waste landfill were removed up to 32% and 68%, respectively, at addition of 490 mgAlum/L and 1,000 mgPAC/L in adsorption-coagulation process with pH control. Combined adsorption and coagulation process with pH control showed better COD and color removal than the process without pH control. The color removal was influenced greatly by pH control, while COD removal was not. No difference in removal efficiency was observed between adsorption-coagulation and coagulation-adsorption. Maximum net increases in the COD and color removals by the adsorption-coagulation process were 40% and 46%, respectively, compared with the removals by sole chemical precipitation. The Freundlich isotherm exclusively described the adsorption of leachate components on the PAC. Thus, a combined adsorption and coagulation process was considered to be effective for pre-treatment or post-treatment of landfill leachate, and has distinct features of simple, flexible, stable and reliable operation against fluctuation of leachate quality and flowrate.     

膜生物反应器处理垃圾渗滤液问题分析

针对目前垃圾渗滤液用膜生物反应器（MBR）系统处理效果不佳、运行不稳定的问题,通过理论模型预测分析了渗滤液系统MBR的污泥浓度及其构成。结果表明垃圾焚烧厂的渗滤液MBR存在污泥浓度过高（22．0g／L）的问题,如果采用厌氧微网预处理则能将污泥浓度降低约50％,可大大提高MBR的运行稳定性。填埋场渗滤液MBR则存在处理年轻期渗滤液污泥浓度过高,而污泥浓度和污泥活性会随填埋龄增加迅速下降的问题,建议采取必要的预处理措施降低年轻期渗滤液的污染物负荷,改善中、老年期渗滤液的可生化性能,提高以MBR为主体的垃圾渗滤液处理工艺的运行稳定性。     

ACIDOGENIC FERMENTATION OF LIGNOCELLULOSIC SUBSTRATE WITH ACTIVATED SLUDGE

The lignocellulosic residues accumulated in municipal solid waste and agro-residues represent potential organic fractions preferably to be treated by anaerobic digestion in an energy recycle and/or value-added-product-type solid waste disposal system. Hydrolysis and acidification are predominant reactions in organic fermentation. Owing to the complicated physiochemical structures, the initial hydrolysis and acidification of the lignocellulosic residues into soluble forms are critical to the anaerobic digestion of the residues. This research focused on the promotion of solid-state acidogenic fermentation of two natural lignocellulosic residues in a pure form from the tobacco industry and urban turf grass by a combined pretreatment and thermophilic co-digestion with concentrated activated sludge from a biological municipal wastewater treatment plant. Laboratory-scale experiments were conducted in a batch and semi-continuous mode, with and without leachate recirculation. The results showed that the mechanophysicochemical pretreatment (roll milling-freezing-thawing-alkali wetting agent), followed by thermophilic co-digestion with activated sludge, substantially increased the solubility and fermentation efficiency of the natural lignocellulosic residues, leading to value-added utilization of these residues. In addition, leachate recycling appeared to be beneficial to acidogenesis.     

污泥预处理-厌氧消化体系的能源经济性评价

在污泥的厌氧消化中，降低过程能耗与提高甲烷产量是实现污水处理系统“碳中和”的主要思路之一。热、化学、机械预处理是打破厌氧消化限速水解的有效手段，主要着眼于甲烷增产以形成更多的“碳补偿”。但从热力学角度，预处理是通过消耗电能、热能、化学能使有机物大量溶解，从而获得更多生物质能的过程，其本身作为一种能量输入形式增加了厌氧消化的能耗。以往的研究通常以污泥液相中有机物溶出、固相中有机物去除以及甲烷产量作为厌氧消化性能的评价指标，难以客观评估各类厌氧消化预处理的实际效益。本文从能源转换的角度出发，综述了各类污泥预处理方法的作用机理及对厌氧消化的抑制因子等方面的研究进展，对比了典型的热预处理、碱预处理、超声预处理及其联合处理分别在甲烷产量、净能量和净利润等指标上的研究结果，并在污泥厌氧消化效率评价基础上分析了上述预处理方法在能源和经济层面的可行性，为预处理方法和预处理条件的选择提供多维度依据。     

改善污泥厌氧消化性能的预处理技术

厌氧消化是污泥稳定化处理的主要技术之一。通过采用一定的预处理技术，破坏细胞结构，释放有机质，促进污泥的水解速率，从而改善污泥厌氧消化性能。该文综述了几种国内外目前研究较为广泛的预处理技术，主要包括热预处理法、转动球磨法、高压喷射法、超声波预处理法、酸预处理法、碱预处理法和氧化法等技术，并分别探讨了各种技术的作用原理、特点、处理效果及应用前景。     

Anaerobic Treatment of Leachates in a Pilot-Scale UASB: Strategy of Start-up

The anaerobic digestion of leachates from a solid urban wastes landfill was studied using an upflow anaerobic sludge blanket reactor in pilot scale. The strategy of start-up and acclimation was based on gradual substitution of easily biodegradable feed with landfill leachate. All modifications were based on the attainment of 70% COD removal. Having completed the start-up, the kinetics of leachate biodegradation were studied and the values of kinetic parameters were obtained by fitting experimental data to the equation of Chen and Hashimoto. The biodegradability assays indicated that 40–50% of COD in leachate was biodegradable. The highest COD removal was 90–100% if only the biodegradable matter was considered.     

Effect of sonolysis on waste activated sludge solubilisation and anaerobic biodegradability

Activated sludge processes are key technologies in wastewater treatment. These biological processes produce huge amounts of waste activated sludge (WAS) or otherwise biosolids. Mechanical, thermal, and/or chemical WAS conditioning techniques have been proposed to reduce the sludge burden. Among the WAS treatments, the pre-treatment with ultrasound (US) is one of the most innovative processes. In many anaerobic digestion processes for the treatment of the sludge produced in wastewater treatment plants, the hydrolysis of the organic matter has been identified as the rate limiting step.This study is focused on the effect of US pre-treatment of WAS to the anaerobic digestion. Particle size reduction, Chemical Oxygen Demand (COD) solubilization and biodegradability by anaerobic digestion were monitored in order to find the optimal dose in US pre-treatment.The results show the better sonolysis conditions (US density, sonication time, specific energy) which can significantly improve the COD solubilisation and the anaerobic biodegradability.     

Combined Ozone Pretreatment and Anaerobic Digestion for the Reduction of Biological Sludge Production in Wastewater Treatment

The ever-increasing amount of solid waste generated by wastewater treatment plants highlights emerging economic and environmental issues. In order to develop new processes producing less sludge, the use of ozone combined with anaerobic digestion was investigated for waste activated sludge treatment. This paper was aimed at evaluating the impact of ozone pretreatment on anaerobic digestion and particularly the enhancement of biogas production. Sludge solubilization was estimated in terms of modification of chemical oxygen demand, solids and nitrogen. Batch anaerobic digestion highlighted the enhancement of ozonated sludge biodegradability. Ozonation led to an increase in biogas production. The ozone dose of 0.15 g O₃/g total solids resulted in a considerable increase in the soluble COD ratio from 4% to 37%. This ozone dose achieved the highest increase in biogas production: 2.4 times greater than without chemical pretreatment.     

Enhancement of Coagulation Flocculation Process Using Anionic Polymer for the Post Treatment of UASB Reactor Effluent

This study was conducted for the treatment of up-flow anaerobic sludge blanket (UASB) reactor effluent by polymer assisted coagulation–flocculation process. The efficiency of alum, FeCl₃, and polyaluminum chloride (PAC) was observed alone and in coupled with anionic polymer (Synpol). The results revealed that FeCl₃ and PAC are efficient to remove 99% of turbidity, 83% of total suspended solids (TSS), 82% and 85% of biochemical oxygen demand (BOD) and chemical oxygen demand (COD), respectively, and 99.5% removal of total coliforms (TC) and fecal coliforms (FC). The addition of anionic polymer to alum, FeCl₃, and PAC reduces the sludge volume upto 25%.     

活性炭提高膜生物反应器运行性能的研究进展

通过投加粉末活性炭(PAC)/颗粒活性炭(GAC)改善污泥混合液性质从而减缓膜污染是膜生物反应器(MBR)领域的研究热点,重点介绍了最近五年有关活性炭与MBR结合处理不同类型废水的研究进展,投加PAC/GAC对MBR处理能力的影响,对减缓膜污染的作用,尤其是结合动态膜(DM)论述对污泥性质的改善.重点讨论了活性炭在好氧...     

Addition of activated carbon to batch activated sludge reactors in the treatment of landfill leachate and domestic wastewater

Leachate from a municipal landfill was combined with domestic wastewater and was treated in batch activated sludge systems. The effectiveness and applicability of the addition of Powdered Activated Carbon (PAC) to activated sludge reactors was investigated. Isotherm tests were carried out with PAC in order to estimate the extent of adsorption of organic matter onto PAC. Then, in activated sludge reactors COD (Chemical Oxygen Demand) removal and nitrification were studied both in the absence and presence of PAC for comparison purposes. In both cases, Oxygen Uptake Rates (OUR) were measured with respect to time in order to investigate substrate removal and change in microbial activity. Addition of PAC to activated sludge increased COD removal by removing mainly the non‐biodegradable fraction in leachate. The COD decreases in batch reactors were best expressed by a first‐order kinetic model that incorporated this non‐biodegradable leachate fraction. With added PAC, nitrification was also enhanced. But in all of the batch runs a significant accumulation of NO₂ ‐N took place, indicating that the second step of nitrification was still inhibited. © 2001 Society of Chemical Industry     

碱预处理耦合零价铁强化含油污泥厌氧消化

含油污泥通常含较多的生物难降解性有机化合物,且污泥黏度大,乳化程度高,导致其厌氧消化潜力较低。污泥细胞破壁较慢,是污泥厌氧消化的限速步骤。本研究通过对含油污泥进行碱预处理,实现了污泥细胞破壁,并检测到胞内有机物质大量溶出,进而加快污泥水解为溶解态的小分子有机物,提高厌氧消化效率。另一方面,为了解决由预处理产生过量有机酸（如丙酸等）积累破坏厌氧系统内pH平衡的问题,本研究通过投加零价铁,促进丙酸等小分子向乙酸的转化,促进产甲烷,并最终使厌氧系统内pH保持平衡。研究结果表明：含油污泥经过碱预处理甲烷产量提高91.7%,同时污泥减量率提高了8%。碱预处理耦合零价铁粉,使得甲烷产量提高了105.4%,污泥减量率提高13%。进一步优化碱预处理pH条件,结果表明碱处理的最佳pH为9。     

Optimum Process Parameters for the Treatment of Landfill Leachate Using Powdered Activated Carbon Augmented Sequencing Batch Reactor (SBR) Technology

The sequencing batch reactor (SBR) process was used for the treatment of raw landfill leachate. Optimum preliminary parameters of leachate/activated sludge ratio, powdered activated carbon (PAC) dosage, and settling time were studied. Optimum obtained parameters (mixing ratio of 10%, PAC dosage of 10 g/L, and settling time of 1.5 h) were applied on two types of SBRs, namely, non-powdered and powdered activated carbon (NPAC and PAC, respectively). Consequently, the effect of factors, the aeration rate and contact time, on both NPAC and PAC reactors were studied. Response surface methodology was used for the design, analysis, and optimization of the experiments. Removal efficiencies of ammonia (NH₃-N), color, chemical oxygen demand (COD), total dissolved salts (TDS), and sludge volume index (SVI) were measured for 13 experiments. Based on the obtained results, the optimum aeration rate and contact time for both NPAC and PAC reactors were 2 and 1 L/min and 5.56 and 5.5 h, respectively. Better performance (in terms of NH₃-N, color, COD, and TDS removal efficiencies and SVI values) was exhibited by PAC reactors rather than NPAC.     

Effect of coagulation on palm oil mill effluent and subsequent treatment of coagulated sludge by anaerobic digestion

A new effluent treatment scheme is proposed for treating palm oil mill effluent based on coagulation and anaerobic digestion of coagulated sludge. The effectiveness of anionic (N9901) and cationic (N9907) polyelectrolytes manufactured by NALCO (Malaysia) was evaluated both as coagulant and coagulant aid. The results showed that the anionic and cationic polyelectrolytes were best suited as a coagulant aid, and the cationic polyelectrolyte showed better performance than the anionic polyelectrolyte. For an influent chemical oxygen demand (COD) concentration of 59 700 mg L^?1 at an alum dosage of 1700 mg L^?1, the residual COD, suspended solid removal, sludge volume and pH were found to be 39 665 mg L^?1, 87%, 260 mL L^?1 and 6.3, respectively. For the above influent COD and alum dosage with the addition of 2 mg L^?1 of cationic polyelectrolyte as coagulant aid, the results were 30 870 mg L^?1, 90%, 240 mL L^?1 and 6.2, respectively. The sludge resulting from the coagulation process using alum as coagulant and cationic polyelectrolyte as coagulant aid was tested for its digestibility in an anaerobic digester. The quantity of biogas generated per gram of volatile solids (VS) destroyed at a loading rate of 26.7 ± 0.5 and 35.2 ± 0.4 g VS L^?1 d^?1 was found to be 0.68 and 0.72 L g^?1 VS destroyed. The anaerobic biomass when subjected to varying alum dosage in the coagulated palm oil sludge did not exhibit inhibition as the digester performance was in conformity with the regular treatment process Copyright © 2006 Society of Chemical Industry     

Anaerobic digestion of waste activated sludge—comparison of thermal pretreatments with thermal inter‐stage treatments

BACKGROUND: Treatment methods for improved anaerobic digestion (AD) of waste activated sludge were evaluated. Pretreatments at moderate thermal (water bath at 80 °C), high thermal (loop autoclave at 130–170 °C) and thermo‐chemical (170 °C/pH 10) conditions prior to AD in batch vials (40 days/37 °C) were compared with inter‐stage treatments under the same conditions carried out between two separate steps of AD (19–21 days/37 °C). Combined treatment at 80 °C with CO₂/ NH₃‐stripping was also evaluated. RESULTS: Pretreatment at 80 °C had no effect on methane yield while inter‐stage treatment gave a 20% increase, compared with controls. Combining inter‐stage treatment with CO₂/ NH₃‐stripping gave an increase in pH (7.1 to 9.3), a drop in ammonia‐N concentration (910 mg‐N to 510 mg‐N) and a methane yield improvement of 31%. Pretreatment at 130 °C, 170 °C and 170 °C/pH 10 considerably increased the methane production within the first 4 days but the improvement following 40 days of digestion was only 13%, 9% and 2%, respectively. In comparison, inter‐stage treatment led to improvements of 9% (130 °C), 29% (170 °C) and 28% (170 °C/pH 10). All treatment processes increased sludge solubilization. CONCLUSION: Thermal treatment of waste activated sludge for improved anaerobic digestion seems more effective when applied as an inter‐stage treatment rather than a pretreatment. Copyright © 2010 Society of Chemical Industry     

微波预处理剩余污泥的研究进展

介绍了微波预处理污泥的作用机理及作用过程,包括污泥絮体破解、污泥细胞破碎及有机物的释放、有机物水解、美拉德反应等,总结了微波预处理污泥的作用效果（物理特性、化学特性、生物特性）、影响微波预处理效果的因素（污泥特性、处理条件）和微波预处理污泥对其后续厌氧消化的影响。指出了目前研究中存在的主要问题是试验规模偏小,预处理方式为间歇处理,在对污泥中有毒有害有机物和病原微生物的去除研究方面还需加强。提出今后应重点开展微波组合工艺对污泥中有毒有害有机物和病原微生物去除的基础研究,同时积极开发相关设备,开展微波预处理污泥的连续和中试研究,推动微波技术在污泥资源化、减量化和无害化处理中的应用。     

Anaerobic degradation: the effect of the combined treatment of substrates on the refractory fraction

The anaerobic digestion of landfill leachates mixed with domestic sewage was studied using a batch reactor at laboratory scale. Batch assays were carried out with different proportions of leachate in the feed: 100, 70, 50 and 30% by volume, with and without adjustment of pH, in order to determine the percentage of acidification and methanization, COD removal, anaerobic biodegradability and biomass growth yield. The main effect of the mixing with sewage was a synergistic improvement of the anaerobic treatment of leachates, but in different ways; the greatest improvement in COD removal was obtained when the proportion of leachate in the feed was 70%, but the highest degree of anaerobic biodegradability was obtained with 30% of leachate in the feed. The kinetics of these assays was studied and the experimental data were fitted to a modification of the equation of Chen and Hashimoto. A new concept of ‘non‐biodegradable fraction’ is proposed. © 2002 Society of Chemical Industry     

微塑料对污泥厌氧消化的影响和机理

污泥厌氧消化对实现污水处理厂“碳减排”具有重要意义,然其产甲烷效率和工艺稳定性易受多种因素干扰。微塑料作为新兴污染物经污水处理后,约有99%富集在污泥中,对污泥厌氧消化过程产生影响。因此,本文重点总结了污水中微塑料的来源、性质及其在污水处理工艺中的归宿,详细阐述了聚苯乙烯（PS）、聚酰胺6(PA6)、聚氯乙烯（PVC）等常见微塑料对污泥增溶、水解、酸化和产甲烷阶段的影响,并从细胞结构、微生物群落、酶活性等角度进一步归纳了微塑料影响厌氧消化的机理。最后,在概括当前研究成果的基础上,提出应从系统工程研究（预处理技术、运行条件、反应器类型等）、微塑料及其浸出物的抑制机制（微塑料与胞外聚合物、细胞膜的作用、标志性辅酶和辅因子、特征微生物方面）、微塑料与污泥其他组分间的协同/抑制机理等方面开展深入研究,为污泥资源化利用提供理论基础和技术支持。     

Dry anaerobic batch digestion of the organic fraction of municipal solid waste

Anaerobic digestion at high solid concentrations (dry anaerobic digestion) is an attractive method for the stabilization of solid organic wastes. A new concept for dry anaerobic batch digestion (BIOCEL) of the organic fraction of municipal solid waste is presented. The start up of a BIOCEL reactor was studied with several methods of process set up and operation. Dry anaerobic digestion of the pure undiluted organic fraction obtained from a shredding/separation process was not accelerated by partial spatial separation of substrate and methanogenic inoculum (granular sludge) or leachate recycle, or both. With these three methods after 30 days the high organic acids concentration and low pH in the reactor indicated a sour reactor, unable to establish significant methane production. When the organic fraction was digested in combination with compost addition (40% (w/w) of the initial solids) and leachate recycle, the stabilization rate increased significantly. Leachate recycling in combination with partial spatial separation of the substrate/compost mixture and the inoculum showed the shortest lag phase in the methane production and the shortest digestion time. When the digested residue of a completed digestion was applied as the methanogenic inoculum (40% (w/w) of the initial total solids) the digestion time was slightly shorter. It is concluded that dilution with compost had a positive effect on the start up of the dry anaerobic digestion and compensated for a suboptimal amount of initial methanogenic biomass. During the start up of dry anaerobic batch digestion of municipal solid waste the rapid recovery of methane formation from an initial overloading was observed and was found to be the result of a population shift in the methanogenic biomass and the existence of zones in the reactor with more optimal conditions (higher p H, lower organic acids concentration). The observed digestion time was 36 days. Recommendations are given to shorten the period needed, for complete digestion.     

Evaluation of adsorption and coagulation characteristics of humic acids preceded by alternative advanced oxidation techniques

Humic substances mainly humic acids constitute the major fraction of natural organic matter in water supplies. Humics express diverse actions primarily related to the formation of potentially harmful disinfection by products (DBPs). Therefore, the removal of DBP precursors through numerous treatment techniques gains high importance. Besides the conventional treatment processes, the applications of advanced oxidation techniques are considered as effective tools for the elimination of humic acids (HAs) from natural waters. In the present study, both the adsorption and coagulation characteristics of humic acid samples are evaluated subsequent to pretreatment by photocatalytic oxidation and ozonation. The changes in preoxidized humic acid solutions are assessed in relation to the alterations induced in the UV-vis and fluorescence spectroscopic properties. The removal efficiency of color in terms of Color₄₃₆ and aromaticity with respect to UV₂₅₄ are presented relevant to each treatment step. Major key parameters such as the selection of coagulant types (alum and ferric chloride), coagulant aids (ionic and non-ionic polyelectrolyte) and optimum coagulant dose were comparatively discussed. The adsorption characteristics of powdered activated carbon (PAC) and granular activated carbon (GAC) were investigated.