Effects of acclimated sludge used as seeding material in the start-up of anaerobic digestion of glycerol

Methods for improving the anaerobic digestion of glycerol (propane-1,2,3-triol) were investigated, particularly the effects of using acclimated sludge as seeding material during start-up. Glycerol was supplied to the anaerobic digester at an organic loading rate of 2.5 g-COD L^?1 day^?1. Four experimental runs were carried out with varying mixing ratios of acclimated sludge to unacclimated sludge (0, 10, 20, and 33%). Calculations were performed by employing a numerical model, whose parameters were determined by experimental measurements. Methane production rate (MPR) for all runs attained similar stable values around 21.4 mmol L^?1 day^?1, though more time was required for attaining stable state of methane production with lower mixing ratios of acclimated sludge. The initial MPR calculated was proportional to the mixing ratio of acclimated sludge. Furthermore, molecular biological methods showed that the types of microorganisms observed in all runs were similar. These results indicate that the seeding with different mixing ratios of acclimated sludge did not affect the microbial consortia in the anaerobic digestion approaching stable state, but did affect the cell density of the useful microorganisms at the start of methane fermentation. Consequently, it was confirmed that at a higher mixing ratio of acclimated sludge, the start of methane production became more vigorous.     

Anaerobic treatment of effluents from an industrial polymers synthesis plant

The feasibility of the anaerobic treatment of an industrial polymer synthesis plant effluent was evaluated. The composition of the wastewater includes acrylates, styrene, detergents, a minor amount of silicates and a significant amount of ferric chloride. The average chemical oxygen demand (COD) corresponding is about 2000 mg/l. The anaerobic biodegradability of the effluent is shown and the toxicity effect on the populations of anaerobic bacteria is evaluated. The results of the anaerobic biodegradation assays show that 62% of the wastewater compounds, measured as COD, could be consumed. An upflow anaerobic sludge blanket (UASB) reactor was used in the evaluation, it has a diameter–height ratio of 1:7, and 4-liter volume. The inoculum was obtained from a UASB pilot plant that treats brewery wastewaters. At the beginning of the operation, the biomass showed an anaerobic activity of 0.58 gCOD/(gVSS×d), it decreased only 2.5% in the subsequent 4 months. After 35 days of continuous operation, the reactor was operated at different steady states for 140 days. The COD was maintained at 2200 mg/l in the feed. The results were: organic loading rate (OLR): 4.3 kg COD/(m³×d), hydraulic retention time: 12 h, superficial velocity: 1 m/h, average biogas productivity: 290 L CH₄/kg COD fed, biogas composition: 70–75% methane and a COD removal percentage >75%. ©     

Anaerobic treatment of sludge from a nitrification-denitrification landfill leachate plant

The viability of anaerobic digestion of sludge from a MSW landfill leachate treatment plant, with COD values ranging between 15,000 and 19,400mg O(2)dm(-3), in an upflow anaerobic sludge blanket reactor was studied. The reactor employed had a useful capacity of 9l, operating at mesophilic temperature. Start-up of the reactor was carried out in different steps, beginning with diluted sludge and progressively increasing the amount of sludge fed into the reactor. The study was carried out over a period of 7 months. Different amounts of methanol were added to the feed, ranging between 6.75 and 1cm(3)dm(-3) of feed in order to favour the growth of methanogenic flora. The achieved biodegradation of the sludge using an upflow anaerobic sludge blanket Reactor was very high for an HRT of 9 days, obtaining decreases in COD of 84-87% by the end of the process. Purging of the digested sludge represented approximately 16% of the volume of the treated sludge.     

Composting anaerobic and aerobic sewage sludges using two proportions of sawdust

Sawdust has been proven to be a good bulking agent for sludge composting; however, studies on the most suitable ratio of sludge:sawdust for sludge composting and on the influence of the sludge nature (aerobic or anaerobic) on the composting reaction rate are scarce. In this study two different sewage sludges (aerobic, AS, and anaerobic, ANS) were composted with wood sawdust (WS) as bulking agent at two different ratios (1:1 and 1:3 sludge:sawdust, v:v). Aerobic sludge piles showed significantly higher microbial activity than those of anaerobic sludge, organic matter mineralization rates being higher in the AS mixtures. The lowest thermophilic temperatures during composting were registered when the anaerobic sludge was mixed with sawdust at 1:1 ratio, suggesting the presence of substances toxic to microorganisms. This mixture also showed the lowest decreases of ammonium during composting. All this matched with the inhibitory effect on the germination of Lepidium sativum seeds of this mixture at the first stages of composting, and with its low values of microbial basal respiration. However, the ANS+WS 1:3 compost developed in a suitable way; the higher proportion of bulking agent in this mixture appeared to have a diluting effect on these toxic compounds. Both the proportions assayed allowed composting to develop adequately in the case of the aerobic sludge mixture, yielding suitable composts for agricultural use. However, the ratio 1:1 seems more suitable because it is more economical than the 1:3 ratio and has a lower dilution effect on the nutritional components of the composts. In the case of the anaerobic sludge with its high electrical conductivity and ammonium content, and likely presence of other toxic and phytotoxic substances, the 1:3 ratio is to be recommended because of the dilution effect.     

Anaerobic co-digestion of tannery waste water and tannery solid waste using two-stage anaerobic sequencing batch reactor: focus on performances of methanogenic step

In this study, anaerobic co-digestion of the tannery waste water (TWW) and tannery solid waste (TSW) with four TWW to TSW mixing ratios (100:0, 75:25, 50:50 and 25:75) was carried out using semi-continuous two-phase anaerobic sequencing batch reactor system under mesophilic temperature (38?±?2 °C). During the experimental study, effluents resulted from previously optimized acidogenic reactors were used to feed subsequent methanogenic reactors and then operated at hydraulic retention time (HRT) of 20, 15 and 10 days and equivalent organic loading rate. The findings revealed that methanogenic reactor of 50:50 (TWW:TSW) treating the effluent from previously optimized acidogenic step exhibits best process performances in terms of daily biogas (415 ml/day), methane production (251 ml/day), methane content (60.5%) and COD removal efficiency (75%) when operated at HRT of 20 days. Process stability of methanogenic step also evaluated and the obtained results showed suitable pH (6.8), no VFA accumulation, i.e., VFA/Alkalinity (0.305), alkalinity (3210 mgCaCO₃/l) and ammonia (246 mg/l with in optimum operating range). In general, improved process stability as well as performance was achieved during anaerobic co-digestion of TWW with TSW compared to mono-digestion of TWW.     

Investigations on enhanced in situ bioxidation of methane from landfill gas (LFG) in a lab-scale model

The performance of an exogenous bacterium, Methylobacterium extorquens, in inducing bioxidation of methane from landfill gas (LFG) was assessed in a laboratory scale bioreactor. The study show that enhanced oxidation of methane is attained when the bacteria are introduced into the landfill soil. The maximum percentage reduction of methane fraction from LFG when the bioreactor was inoculated with the methanotrophic bacteria was 94.24 % in aerobic treatment process and 99.97 % in anaerobic process. In the experiments with only the indigenous microorganisms present in the landfill soil, the maximum percentage reduction of methane for the same flow rate of LFG was 59.67 % in aerobic treatment and 45 % in anaerobic treatment. The methane oxidation efficiency of this exogenous methanotrophic bacterium can be considered to be the optimum in anaerobic condition and at a flow rate of 0.6 L/m²/min when the removal percentage is 99.95 %. The results substantiate the use of exogenous microorganisms as potential remediation agents of methane in LFG.     

Extracting humic acids from digested sludge by alkaline treatment and ultrafiltration

The concentration of hardly biodegradable humic substances in sludge would relatively increase after anaerobic digestion due to the degradation of other organic substances. Thus, extracting humic substances from digested sludge as a liquid organic fertilizer was tested using alkaline treatment and ultrafiltration, and the dewaterability of the residual sludge was also tested. The results showed that the contents of humic acids and fulvic acids in digested sludge were 16.4 mg/g total solids and 88.9 mg/g total solids, respectively, and most of the humic acids had a molecular weight higher than 50 kDa. Hence, the membrane with a molecular weight cut-off of 50 kDa was used for humic acids recovery from the centrifugation supernatant after alkaline sludge disintegration with an optimum NaOH dose of 0.1 mol/L. Under these conditions, the total concentration of humic acids and fulvic acids was 4239 mg/L in the retention solution, which can be further concentrated and processed for liquid fertilizer. The total recovery rate of sludge humic acids and fulvic acids was about 25 %. The dewatering performance of the residual sludge was better than that of the untreated sludge when the residual sludge was diluted to a water content of 95–98 % and then conditioned with polyacrylamide at a dose of 10–30 mg/L.     

Enhanced bioleaching efficiency of copper from waste printed circuit boards (PCBs) by dissolved oxygen-shifted strategy in <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis>

Acidithiobacillus ferrooxidans, as chemolithotrophic aerobic bacterium, can obtain energy by oxidation of ferrous ions (Fe²⁺) to ferric ions (Fe³⁺) and use molecular oxygen (O₂) as terminal electron acceptor. In this study, the effects of dissolved oxygen (DO) levels in culture medium on cell growth and copper extraction from waste printed circuit boards (PCBs) were investigated in A. ferrooxidans. The whole culture period was divided into two stages of cell growth and copper extraction. At the former stage, relatively lower DO level was adopted to satisfy bacterial growth while avoiding excessive Fe²⁺ oxidation. At the later stage, higher DO was used to promote copper extraction. Moreover, shift time of DO from lower to higher level was determined via simulating Gauss function. By controlling DO at 10 % for initial 64 h and switching to 20 % afterwards and with 18 g/l PCBs addition at 64 h, final copper recovery reached 94.1 %, increased by 37.6 and 48.3 % compared to constant DO of 10 and 20 % operations. More importantly, copper leaching periods were shortened from 108 to 60 h. It was suggested that application of DO-shifted strategy to enhancing copper extraction from PCBs with reduced leaching periods is being feasible.     

用味精生产废水培养好氧颗粒污泥

以厌氧颗粒污泥为接种污泥,采用味精生产废水进行培养,在SBR中以逐渐降低污泥沉淀时间的方法成功培养出好氧颗粒污泥。实验结果表明：污泥接种65 d后,出现细小的好氧颗粒污泥,呈黄褐色,95 d后颗粒污泥趋于成熟,粒径达0.6 mm左右,且周围存在大量原生动物;运行95 d后MLSS提高至8.00 g/L,SVI降至30.00 mL/g左右;成熟后的好氧颗粒污泥对味精生产废水中的COD和NH₃-N具有良好的去除效果,出水COD和ρ（NH₃-N）分别为80 mg/L和2 mg/L左右。     

Comparison of different liquid anaerobic digestion effluents as inocula and nitrogen sources for solid-state batch anaerobic digestion of corn stover

Effluents from three liquid anaerobic digesters, fed with municipal sewage sludge, food waste, or dairy waste, were evaluated as inocula and nitrogen sources for solid-state batch anaerobic digestion of corn stover in mesophilic reactors. Three feedstock-to-effluent (F/E) ratios (i.e., 2, 4, and 6) were tested for each effluent. At an F/E ratio of 2, the reactor inoculated by dairy waste effluent achieved the highest methane yield of 238.5 L/kgVS_feed, while at an F/E ratio of 4, the reactor inoculated by food waste effluent achieved the highest methane yield of 199.6 L/kgVS_feed. The microbial population and chemical composition of the three effluents were substantially different. Food waste effluent had the largest population of acetoclastic methanogens, while dairy waste effluent had the largest populations of cellulolytic and xylanolytic bacteria. Dairy waste also had the highest C/N ratio of 8.5 and the highest alkalinity of 19.3 g CaCO₃/kg. The performance of solid-state batch anaerobic digestion reactors was closely related to the microbial status in the liquid anaerobic digestion effluents.     

Enhanced anaerobic treatment of CSTR-digested effluent from chicken manure: The effect of ammonia inhibition

The effect of ammonia inhibition was evaluated during the enhanced anaerobic treatment of digested effluent from a 700 m³ chicken-manure continuous stirred tank reactor (CSTR). A 12.3 L internal circulation (IC) reactor inoculated with an anaerobic granular sludge and operated at 35 ± 1 °C was employed for the investigation. With a corresponding organic loading rate of 1.5-3.5 kg-COD/m³ d over a hydraulic retention time of 1.5 d, a maximum volumetric biogas production rate of 1.2 m³/m³ d and TCOD (total COD) removal efficiency ranging from 70% to 80% was achieved. However, the continual increase in the influent TAN content led to ammonia inhibition in the methanogenesis system. The SCOD/TAN (soluble COD/total ammonia nitrogen) ratio was presented to be the key controlling factor for the anaerobic treatment of semi-digested chicken manure, and further validation through shock loading and ammonia inhibition experiments was conducted. The threshold value of the SCOD/TAN ratio was determined to be 2.4 (corresponding to a TAN of 1250 mg/L) at an influent pH of 8.5-9.     

Biodegradation characteristics of organic matters in swine carcasses under different initial operating conditions of simulated anaerobic lysimeter

This study was aimed to investigate the biodegradation characteristics of organic matters in swine carcasses. The lysimeters were simulated with different initial operating conditions: 30 % volumetric moisture content and no sludge addition for lysimeter A (control), 30 % volumetric moisture content and anaerobic sludge addition for lysimeter B, and 40 % volumetric moisture content and anaerobic sludge addition for lysimeter C. The degradation efficiency (18.4 %) of lysimeter B was higher than that (15.2 %) of lysimeter A due to anaerobic sludge addition. Lysimeter B showed higher CH₄ yield (15.6 L/kg VS) and CH₄ production rate (0.41 L/kg VS days) compared to lysimeter A by 31 % and 14 %, respectively. In addition, the degradation efficiency improved from 18.4 % (lysimeter B) to 26.3 % (lysimeter C) by increasing volumetric moisture content. The CH₄ yield (22.9 L/kg VS) and CH₄ production rate (0.68 L/kg VS days) of lysimeter C were higher than those of lysimeter B, respectively. Total organic carbon (TOC) removed in lysimeter C was converted to leachate (20.3 %) and gas (6.0 %), whose values were higher than those of lysimeter A and B. These results demonstrated that the proper control of initial operating conditions could accelerate the anaerobic degradation of organic matters in swine carcasses.     

厌氧氨氧化-反硝化协同脱氮研究

采用厌氧氨氧化（ANAMMOX）工艺的上流式厌氧污泥床（UASB）-生物膜反应器（简称反应器）处理高浓度含氮废水,启动并稳定运行630d后,进行进水浓度负荷实验分析。当进水ρ（NH3-N）,ρ（NO2--N）,ρ（TN）分别为340．0,448．8,788．8mg／L时,其去除率分别为84．0％,93．0％,85．0％。在反应器中连续加入有机物（葡萄糖）,进水ρ（NH3-N）和ρ（NO2--N）分别为240．0,316．8mg／L,进水COD为330．0—380．0mg／L,COD去除率达92．0％。仅用23d,在同一反应器系统中成功实现了ANAMMOX与反硝化协同作用脱氮。葡萄糖的存在对系统去除NH3-N和NO2--N的能力影响不大。     

Effect of long chain fatty acids removal as a pretreatment on the anaerobic digestion of food waste

This study investigated the effect of long chain fatty acids (LCFAs) removal as a pretreatment prior to anaerobic digestion on the production of methane from food waste. The results showed that the anaerobic digestion of food waste containing 1.6 g COD/L of LCFAs was not inhibited (4 days lag-time, 78.3 % methane recovery in 35 days) compared to that of lipid free food waste (3 days lag time, 72.5 % methane recovery in 35 days); however, some unsaturated LCFAs, which are toxic to microorganism, were accumulated in the batch anaerobic digestion reactor. Meanwhile, in a methanogenic activity study, the activity of methanogens was observed to be linearly inhibited by the presence of more than 1 g COD/L of LCFAs. The possibility of the accumulation of unsaturated LCFAs in the reactor should be considered when operating a large-scale continuous system.     

Fate and behavior of selected heavy metals with mercury mass distribution in a fluidized bed sewage sludge incinerator

In this paper, emission and distribution behavior of six heavy metals (As, Cd, Cr, Ni, Pb, and Hg), particulate matter and mass distribution of mercury within the different streams of a fluidized bed sewage sludge incinerator are presented. At the inlet of air pollution control devices (APCDs); Cd, Cr, Ni and Pb were mainly enriched in coarse particles; comparatively As content was higher in fine particles (<PM_2.5). The concentration of heavy metals in total particulate matter and PM_2.5, at the inlet of APCDs, were in the order of Cr > Ni > Pb > As > Cd. Mercury was almost always distributed in flue gas. Metals, other than mercury, were efficiently removed in APCDs and their concentrations in bottom ash, with fly ash being higher, whereas for that in wastewater, then waste sand was lesser. Overall mercury removal efficiency of APCDs was 98.6 %. More than 83.3 % of mercury was speciated into oxidized form at the inlet of APCDs, attributed by higher chlorine content in sludge. Mercury was mainly distributed in wastewater (78.4 %), wastewater from a spray dry reactor (16.8 %), fly ash in a hopper (3.4 %) and flue gas (1.4 %). This result is one of the first for data to be obtained; more experiments are required to control emission from such sources.     

Simultaneous removal of COD and ammonium from landfill leachate using an anaerobic-aerobic moving-bed biofilm reactor system

The performance of a moving-bed biofilm reactor (MBBR) system with an anaerobic-aerobic arrangement was investigated to treat landfill leachate for simultaneous removal of COD and ammonium. It was found that the anaerobic MBBR played a major role in COD removal due to methanogenesis, and the aerobic MBBR acted as COD-polishing and ammonium removal step. The contribution of the anaerobic MBBR to total COD removal efficiency reached 91% at an organic loading rate (OLR) of 4.08 kgCOD/(m3d), and gradually decreased to 86% when feed OLR was increased to 15.70 kgCOD/(m3d). Because of the complementary function of the aerobic reactor, the total COD removal efficiency of the system had a slight decrease from 94% to 92% even though the feed OLR was increased from 4.08 to 15.70 kgCOD/(m3d). Hydraulic retention time (HRT) had a significant effect on NH+4-N removal; more than 97% of the total NH+4-N removal efficiency could be achieved when the HRT of the aerobic MBBR was more than 1.25 days. The anaerobic-aerobic system had a strong tolerance to shock loading. A decrease in COD removal efficiency of only 7% was observed when the OLR was increased by four times and shock duration was 24 h, and the system could recover the original removal efficiency in 3 days. The average sludge yield of the anaerobic reactor was estimated to be 0.0538 gVSS/gCOD rem.     

两相厌氧+A/O工艺处理腈纶和丙烯酰胺混合废水

采用两相厌氧+A/O工艺处理腈纶和丙烯酰胺混合废水。实验结果表明：在混合进水中V（腈纶废水）∶V（丙烯酰胺废水）=1、产酸反应器HRT为20 h、产甲烷反应器HRT为36 h、A/O池HRT为24 h、DO为4~5 mg/L、混凝池进水COD为（4 000±300） mg/L的条件下,总COD去除率为87%~89%,A/O池出水COD低于500 mg/L,出水达到GB 8978—1996《污水综合排放标准》中的三级标准;在混凝池进水BOD₅/COD为0.20~0.30的条件下,产甲烷反应器出水BOD₅/COD为0.55~0.65,说明两相厌氧可明显提高废水的可生化性。     

好氧颗粒污泥脱氮性能研究

研究了序批式反应器的污泥沉降时间、曝气速率、水力停留时间、进水方式等参数对好氧颗粒污泥的性能以及COD,NH4^*—N,TN去除率的影响。研究结果表明,在一个运行周期内,反应器运行工艺参数,如DO质量浓度和pH,具有一定的变化规律,并且其变化与反应器内各物质的转化存在严格的对应关系。因此,参照反应器运行工艺参数的特征点,对反应过程进行必要的控制,可达到较理想的处理效果。     

Stabilization of sewage sludge in the presence of nanoscale zero-valent iron (nZVI): abatement of odor and improvement of biogas production

The potential benefits of nanoscale zero-valent iron (nZVI) on sludge stabilization, either the abatement of odor or the improvement of biogas production, were investigated in this study. Two commercial-grade microscale iron powders were also utilized for comparison. Adding 0.10 wt% of nZVI in sludge during anaerobic incubation significantly reduced the concentration of H₂S in biogas by 98.0 % (96.2–98.9 %), probably attributed by reactions between sulfides and the neo-formed hydrous Fe(II)/Fe(III) oxides layer at the surface of ZVI nanoparticles. Meanwhile, the percentage of P in bioavailable fractions decreased from 76.8 to 52.5 %, possibly due to the formation of vivianite [Fe₃(PO₄)₂]. Furthermore, 0.10 wt% of nZVI in anaerobic digestion for 17 days enhanced the concentration of CH₄ in biogas by 5.1–13.2 % and improved the production of biogas and methane by 30.4 and 40.4 %, respectively. The amendment of iron nanoparticles during anaerobic digestion can not only effectively reduce H₂S in biogas, but also potentially boost methane production significantly.     

Investigating the performance of aerobic,semi-aerobic,and anaerobic bioreactor landfills for MSW management in developing countries

Three different laboratory bioreactors, each duplicated, with dimensions 0.5 × 0.5 × 1 m were set up and monitored for 160 days. Municipal Solid Wastes with an organic content of ~80 % and a density of 550 kg/m³ were placed in bioreactors. Fresh leachate collected from waste collection vehicles was used with a recirculation rate of 28 L/day. Aerobic bioreactors were aerated at a rate of 0.15–0.24 L/min/kg of waste. Almost the same level of treatment was observed in terms of chemical oxygen demand reduction of leachate, which was in the range of 91–93 %. However, for anaerobic bioreactor, it took almost twice the time, 160 vs. 76 days, to reach the same level of treatment and stabilization. The behavior of semi-aerobic bioreactor was somewhere between the aerobic and anaerobic ones. Total biogas production for anaerobic bioreactors was 90 L/kg of waste, which contained 57–63 % methane. Methane concentration measured in semi-aerobic bioreactor was below 5 %. The main advantage of aerobic bioreactor was the fast rate of the process, while for semi-aerobic bioreactor, it was the elimination of the need for energy to maintain aerobic conditions, and for anaerobic bioreactor it was the production of biogas and potential energy recovery.