Nitrification of centrate from dewatering of anaerobically digested sludge

Nitrification of anaerobically digested sludge centrate was studied in bench-scale suspended growth and fixed film enhanced suspended growth systems at temperatures of 10.5-28.5°C and pH values of 6.0-9.1. Nitrification followed zero-order kinetics in both systems, and ammonia removals in excess of 99% were observed. The temperature dependency of the suspended growth nitrification rate observed under not fully acclimated biomass conditions at pH between 6.8 and 8.5, was expressed as k_T = k₂₀θ^T-20where k₂₀ and θ were found to be 0.34 mg NH₃-N/MLVSS-d and 1.033, respectively. The nitrification rate in the fixed film enhanced suspended growth system involving styrofoam pads ranged from 0.11 to 0.13 mg NH₃-N/mg MLVSS-d at temperatures of 21.5-25°C and pH values of 7.8-8.6. The process contained suspended solids in the range of 10-20 mg/l.     

Heavy metals removal from anaerobically digested sludge by chemical and microbiological methods

The metal removal from anaerobically digested sludge was studied by chemical treatment and microbial leaching processes in laboratory reactors. The removal of metals increased with decreased sludge solid concentration and pH. In the acid treatment process, a pH of 1.5 was required to reduce the copper concentration in the sludge to an acceptable level. In the microbial processes mixed culture gave 10% better solubilisation of metals than in single culture. The acid requirement was lower for the microbial process. The cost of sludge treatment in terms of chemicals was found to be decreased by 80% in microbial leaching.     

Removal of heavy metals from anaerobically digested sewage sludge by isolated indigenous iron-oxidizing bacteria

The removal of heavy metals (Cr, Cu, Zn, Ni and Pb) from anaerobically digested sludge from the Yuen Long wastewater treatment plant, Hong Kong, has been studied in a batch system using isolated indigenous iron-oxidizing bacteria. The inoculation of indigenous iron-oxidizing bacteria and the addition of FeSO4 accelerated the solubilization of Cr, Cu, Zn, Ni and Pb from the sludge. pH of the sludge decreased with an increase in Fe2+ concentrations and reached a low pH of 2-2.5 for treatments receiving both bacterial inoculation and FeSO4. After 16 days of bioleaching, the following heavy metal removal efficiencies were obtained: Cr 55.3%, Cu 91.5%, Zn 83.3%, Ni 54.4%, and Pb 16.2%. In contrast, only 2.6% of Cr, 42.9% of Cu, 72.1% of Zn, 22.8% of Ni and 0.56% of Pb were extracted from the control without the bacterial inoculation and addition of FeSO4. The residual heavy metal content in the leached sludge was acceptable for unrestricted use for agriculture. The experimental results confirmed the effectiveness of using the isolated iron-oxidizing bacteria for the removal of heavy metals from sewage sludge.     

Bioleaching of zinc and copper from anaerobically digested swine manure: effect of sulfur levels and solids contents.

Anaerobically digested swine manure (ADSM) generally contains high concentrations of zinc (Zn) and copper (Cu). These metals levels exceed the land application regulations of municipal biosolids of many European countries and are on the borderline of exceptional quality in the U.S. Environmental Protection Agency (U.S. EPA) 40 CFR part 503 standards. From this perspective, a series of batch tests were conducted to evaluate the feasibility of bioleaching of Zn and Cu from ADSM so that the produced biosolids could safely be applied to land. The effect of different substrate levels (sulfur) and total solids content (as high as 9%) on metal solubilization was investigated. The results showed that metal solubilization efficiency for both Zn and Cu declined significantly with an increase in total solids from 3 to 6% and then to 9% at the same substrate level. Metal solubilization increased proportionately with increases in substrate concentration up to 6% of total solids content. However, at 9% total solids content, metal solubilization was insignificant at all substrate levels tested. At a 6% total solids level and 10 000 mg/L of substrate, 94% of Zn and 72% of Cu were solubilized. Bioleaching was also found to be effective in destruction of pathogens with approximately 2.5 log-scale reduction. The residual biosolid was found to meet the Class A biosolids standands of U.S. EPA 40 CFR part 503.     

Bioleaching of heavy metals from anaerobically digested sewage sludge using FeS2 as an energy source

The effect of using FeS2 as an energy source, on the bioleaching of heavy metals (Zn, Cr, Cu, Pb and Ni) and nutrients (nitrogen and phosphorus) from anaerobically digested sludge using isolated indigenous iron-oxidizing bacteria was investigated in this paper. Addition of FeS2 in the range of 0.5-4.0 g l(-1) accelerated the acidification of sludge and raised the oxidation-reduction potential of sludge medium with an inoculation of 15% (v/v) of active bacteria, thus resulting in an overall increase in metal dissolution efficiency. After 16 days of bioleaching at 28 degrees C and an initial pH of 3.0, up to 99% of Zn, 65% of Cr, 74% of Cu, 58% of Pb and 84% of Ni can be removed from the sludge. In contrast, only 94% of Zn, 12% of Cr, 21% of Cu, 32% of Pb and 38% of Ni were leached out in the control without inoculation of iron-oxidizing bacteria and the addition of FeS2. Less than 15% of nitrogen and 6% of phosphorous were lost after 16 days of bioleaching when using FeS2 as the energy source. Comparing to 39% and 45% loss respectively for these two nutrients when using FeSO4.7H2O as the energy source, FeS2 appears to be a more suitable energy source for preserving nutrients in sludge while removing heavy metals from sludge.     

Degradation of inhibitory substances by heterotrophic microorganisms during bioleaching of heavy metals from anaerobically digested sewage sludge

The presence of organic acids was found to be inhibitory to the bioleaching of sewage sludge and the objective of the present study was to elucidate the roles of heterotrophic microorganisms in removing organic acids during the bioleaching of heavy metals from anaerobically digested sewage sludge. Microbiological analysis showed that acetic and propionic acids posed a severe inhibitory effect on iron-oxidizing bacteria as reflected by a sharp decrease in their viable counts in the first 4d and it only started to increase 2d after the depletion of both acids. Biodegradation of these inhibitory organic acids was revealed by sharp increases in total fungi and acidophiles between day 3 and day 5 which coincided with degradation of organic acids. This was further confirmed by the increases in total counts of both acetate and propionate degraders in the same period. Two yeast strains Y4 and Y5 with strong ability to degrade acetate and/or propionate were isolated and identified as Pichia sp. and Blastoschizomycetes capitatus, respectively. B. capitatus Y5 was an more important player in removing the inhibitory organic acids during the bioleaching process since it could utilize both acetate and propionate as sole carbon source while Pichia sp. Y4 was an strict acetate degrader. Results from the present study not only provided the evidence for biodegradation of organic acids by heterotrophs, but also disclosed a biological mechanism for the initiation of bioleaching of organic acid-laden sewage sludge.     

Cycling of volatile organic sulfur compounds in anaerobically digested biosolids and its implications for odors.

The objectives of this research were to elucidate the mechanisms for production and degradation of volatile organic sulfur compounds (VOSCs), key odor causing compounds produced by biosolids. These compounds included methanethiol (MT), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS). A series of experiments were used to probe various pathways hypothesized to produce and degrade these VOSCs. The production of MT was found to mainly occur from degradation of methionine and the methylation of hydrogen sulfide. DMS was formed through the methylation of MT. DMDS was formed by MT oxidation. All three of the VOSCs were readily degraded by methanogens and a cyclic pathway was proposed to describe the production and degradation of VOSCs. The research demonstrated that the main source of VOSCs was the biodegradation of protein within the biosolids and the results provided a framework for understanding the production of odor from anaerobically digested sludges before and after dewatering.     

Overcoming challenges to struvite recovery from anaerobically digested dairy manure

Recovering struvite from dairy manure has consistently posed problems for researchers. This study separated solids from anaerobically digested dairy manure using a filtration system. Filtrate was rich in free magnesium (160 to 423 mg/L), ammonium (320 to 1800 mg N/L) and orthophosphate (93 to 332 mg P/L). High concentrations of free calcium (128 to 361 mg/L) and alkalinity (3309 to 6567 mg/L as CaCO3), however, may hinder struvite precipitation. Batch precipitation tests were conducted to identify and overcome factors that interfere with struvite formation. Precipitation tests at pH 9 identified calcium and ionic strength as most probable interferences. Calcium addition did not significantly change phosphorus removal efficiency, but decreased struvite purity because of formation of calcium phosphates when Ca:P activity ratio was greater than 0.5 to 1. Batch tests demonstrated effective calcium removal from anaerobically digested dairy manure through precipitation of calcium carbonate at pH 9 to 10 while retaining magnesium and orthophosphate, lessening hindrance to struvite formation.     

硫化物废水形成生物脱硫污泥中单质硫的回收

针对生物脱硫污泥中单质硫回收困难的问题,以生物脱硫系统产生的污泥为实验对象,研究了生物硫污泥的特性。经过测定得到了如下结果:生物脱硫污泥中单质硫的含量为51.2%,蛋白质5%、Na+ 8.32%、Ka+ 7.47%、Mg2+ 4.82%、SO42-10.5%、Cl-4.45%和灰分8.24%,单质硫被带电聚合物所包裹。根据污泥的特性,设计了一套高温溶解-低温析出的单质硫回收工艺。生物硫污泥和萃取剂(甲苯/四氯乙烯=5/95)在80℃下萃取30 min,萃取剂的用量为20 mL/g生物硫污泥,萃取完成后高温过滤,滤液在4℃下过夜保存,再次过滤析出的单质硫晶体。单质硫的回收率为91.2%,析出的单质硫纯度可达98%,可以直接用于其他工业。萃取剂重复使用5次后单质硫的回收率仍可达到79.6%。结果表明,高温溶解-低温析出法可有效从含硫化合物产生的生物硫污泥中提取单质硫。     

Pyrolysis of humic acids from digested and composted sewage sludge

Humic acids (HAs) were extracted from four digested sewage sludge samples composted for four months, one, two and four years. HAs were pyrolyzed at three different temperatures applying both conventional and in situ methylation (ISM) pyrolysis. The pyrolysates were analyzed using gas chromatography-mass spectrometry (GC/MS). Derivatization (ISM) and pyrolysis temperature had dramatic effects on the composition and relative amounts of the pyrolysates. Among the derivatized HA fragments aliphatic compounds prevailed under all the pyrolysis conditions tested. Aromatic substances consisting mainly of guaiacyl-type compounds were detected in higher abundances only at elevated temperatures. Without ISM the contribution of aromatic structures to the total pyrogram was considerably greater than that of the aliphatics. Increase of the pyrolysis temperature from 450 degrees C to 600 degrees C had smaller effect on the proportions and composition of the compounds studied than increase from 350 degrees C to 450 degrees C.     

Optimising the preparation of activated carbon from digested sewage sludge and coconut husk.

Preparation of activated carbon from sewage sludge is a promising way to dispose of sewage sludge as well as to produce a low-cost adsorbent for pollutant removal. This research work aimed to optimise the condition for activated carbon preparation from anaerobically digested sewage sludge with the additive coconut husk. The sewage sludge sample was mixed with the additive coconut husk. The preparation condition variables investigated involved the concentration of the ZnCl2 solutions, heating temperature, dwell time and heating rate in pyrolysis and the mixing ratio of coconut husk to sewage sludge. Surface area, pore size distribution, aqueous phenol adsorption capacity and the production yield of the final products were determined and compared. Experimental results revealed that low concentrations of ZnCl2 solution tended to improve the microporosity of the final product. Heating temperature had a considerable impact on the surface area, pore size distribution and phenol adsorption capacity of the final products, whereas dwell time and heating rate performed comparatively insignificantly. The effect of increasing the mixing ratio of coconut husk to sewage sludge was principally to increase the microporosity of the final products. The activated carbon with the highest BET surface area was produced with the activation of 5 M ZnCl2 solution and, thereafter, pyrolysis at a heating temperature of 500 degrees C for 2 h with a heating rate of 10 degrees C/min. The mixing ratio of 1:4 in terms of coconut husk to sewage sludge based on their dried weights was found to be most cost effective.     

Phosphate removal from digested sludge supernatant using modified fly ash

The removal of phosphate in digested sludge supernatant by modified coal fly ash was investigated in this study. Modification of the fly ash by the addition of sulfuric acid could significantly enhance its immobilization ability. The experimental results also showed that adsorption of phosphate by the modified fly ash was rapid with the removal percentage of phosphate reaching an equilibrium of 98.62% in less than 5 minutes. The optimum pH for phosphate removal was 9 and the removal percentage increased with increasing adsorbent dosage. The effect of temperature on phosphate removal efficiency was not significant from 20 to 40 degrees C. X-ray diffraction and scanning electron microscope analyses showed that phosphate formed an amorphous precipitate with water-soluble calcium, aluminum, and iron ions in the modified fly ash.     

Role of protein, amino acids, and enzyme activity on odor production from anaerobically digested and dewatered biosolids.

The main objective of this research was to test the hypothesis that bioavailable protein and, more specifically, the sulfur-containing amino acids within the protein, can be degraded by proteolytic enzymes to produce odor-causing compounds--mainly volatile sulfur compounds (VSCs)--during biosolids storage. To achieve these objectives, samples of digester effluent and cake solids were collected at 11 different wastewater treatment plants in North America, and the samples were analyzed for protein and amino acid content and general protein-degrading enzyme activity. At the same time, cake samples were stored using headspace bottles, the concentration of VSCs were measured using gas chromatography, and olfactometry measurements were made by a trained odor panel. The results showed that the bound cake protein content and methionine content was well-correlated with VSC production and the detection threshold measured by the odor panel.     

A comparative study of anaerobically digested and undigested sewage sludges in preparation of activated carbons.

Disposal of sewage sludge is an increasingly expensive and environmentally sensitive problem throughout the world. Preparation of activated carbon from sewage sludge offers an attractive re-use alternative to the traditional disposal routes. The objective of this research work was to compare anaerobically digested sewage sludge (DS) and undigested sewage sludge (US) as source materials in the preparation of activated carbons. Prior to the preparation the properties of the two types of sewage sludges were determined and compared. Subsequently the sludge samples were activated with 5 M ZnCl2 solution and thereafter pyrolysed at heating temperature of 650 degrees C for 2 h with the heating rate of 15 degrees C/min under a nitrogen atmosphere. The produced activated carbons were characterised by surface area and porosity analysis, CHN elemental composition and ash contents determination, and aqueous phase phenol adsorption tests. The results indicate that in comparison with the DS, the US had a higher carbon content and lower ash content, and accordingly yielded a better activated carbon with a higher BET surface area, pore volume, carbon content and phenol adsorption capacity.     

A novel use of anaerobically digested liquid swine manure to potentially control soybean cyst nematode

Experiments were carried out in two steps to determine the effect of anaerobically digested swine manure on soybean cyst nematode (SCN) egg control. In the first step, liquid swine manure underwent anaerobic digestion to search for the best digestion time for both volatile fatty acids (VFA) and ammonium nitrogen (NH₄ ⁺) enrichment. The results showed that about 17 and 28 days of incubation were needed, respectively, to reach the maximal levels of VFA and NH₄ ⁺ in the manure. In the second step, raw, VFA-enriched, and NH₄ ⁺-enriched manure were applied separately, at four different rates (25, 50, 100, and 200 mL/pot), to soil pots inoculated with nematode eggs in a greenhouse environment. Soil samples were collected 35 and 61 days after inoculation to determine the effect of such treated manure on SCN egg productivity. The data indicated that the SCN egg counts were inversely related to the manure application rates in a linear manner with correlation coefficients of 0.998, 0.967, and 0.900 for raw, NH₄ ⁺-enriched, and VFA-enriched manure for the 35-day samples. While no such relationships were found for the 61-day samples, implying that none of the treatments were still effective 61 days after application. At the four application rates, the VFA-enriched manure performed best in reducing SCN egg counts (by 18.1, 19.5, 34.3, and 18.6%) as compared to the raw manure treatment. In contrast, the NH₄ ⁺-enriched manure achieved mostly negative reductions. To achieve the best control of SCN egg growth, the VFA-enriched manure should be used and applied to soybean fields every 35 days.     

无机-有机及物理-化学复合调理对厌氧消化污泥脱水性能的影响

厌氧消化是常用的污泥稳定化处理方法,但污泥经厌氧消化处理后脱水性能恶化。分别用无机-有机复合调理剂和物理-化学复合调理剂对厌氧消化污泥进行调理,考察不同调理方法对污泥脱水性能的影响。结果表明,聚合氯化铝（PAC）、聚合硫酸铁（PFS）和阳离子聚丙烯酰胺（PAM）对厌氧消化污泥的调理效果有限,最优条件下污泥比阻（SRF）分别下降了66.3%、89.2%和67.1%;PAC-PAM复合调理和PFS-PAM复合调理对厌氧消化污泥的调理效果较单种调理剂好,最优条件下SRF分别下降了98.2%和97.6%;稻壳、木屑和草木灰与PAM复合调理对厌氧消化污泥的调理效果较单种调理剂好,最优条件下SRF分别下降了97.3%、97.3%和97.7%。     

Impact of drying and composting procedures on the concentrations of 4-nonylphenols, di-(2-ethylhexyl)phthalate and polychlorinated biphenyls in anaerobically digested sewage sludge

Enhanced treatments of sewage sludge produce a more manageable product for agricultural use by stabilizing the material, removing water, and reducing the possibility of pathogen transfer. We investigated the impact of pilot-scale composting and drying of sludge on physicochemical characteristics and on the concentrations of some organic contaminants. During the 143 day composting procedure, organic matter fell 22% and moisture by half. Concentrations of 4-nonylphenols (4-NPs) fell by 88% and di-(2-ethylhexyl) phthalate (DEHP) by 60%; losses continued throughout the procedure. Losses of total polychlorinated biphenyls (PCBs) were 11%, mostly from the lower molecular weight congeners, suggesting volatilization as the most likely loss mechanism. The drying process was much shorter, 40 days, yet organic matter content decreased by 27% and moisture by 85%. Losses of 4-NPs (39%) and DEHP (22%) were less than in composting and stopped when moisture content became constant. There were no losses of PCBs. Both treatments are simple, practical procedures that reduce the volume of waste and are applicable in situ on farms. Composting would be the method of choice for reducing organic contaminants but requires much longer times than drying.     

A novel use of anaerobically digested liquid swine manure to potentially control soybean cyst nematode

Experiments were carried out in two steps to determine the effect of anaerobically digested swine manure on soybean cyst nematode (SCN) egg control. In the first step, liquid swine manure underwent anaerobic digestion to search for the best digestion time for both volatile fatty acids (VFA) and ammonium nitrogen (NH(4)(+)) enrichment. The results showed that about 17 and 28 days of incubation were needed, respectively, to reach the maximal levels of VFA and NH(4)(+) in the manure. In the second step, raw, VFA-enriched, and NH(4)(+)-enriched manure were applied separately, at four different rates (25, 50, 100, and 200 mL/pot), to soil pots inoculated with nematode eggs in a greenhouse environment. Soil samples were collected 35 and 61 days after inoculation to determine the effect of such treated manure on SCN egg productivity. The data indicated that the SCN egg counts were inversely related to the manure application rates in a linear manner with correlation coefficients of 0.998, 0.967, and 0.900 for raw, NH(4)(+)-enriched, and VFA-enriched manure for the 35-day samples. While no such relationships were found for the 61-day samples, implying that none of the treatments were still effective 61 days after application. At the four application rates, the VFA-enriched manure performed best in reducing SCN egg counts (by 18.1, 19.5, 34.3, and 18.6%) as compared to the raw manure treatment. In contrast, the NH(4)(+)-enriched manure achieved mostly negative reductions. To achieve the best control of SCN egg growth, the VFA-enriched manure should be used and applied to soybean fields every 35 days.     

自然生态系统中含硫气体的产生机理与环境归趋

基于当前可获得的与该课题相关的资料 ,本文综述了陆地生态系统产生挥发性含硫气体的微观和宏观机理过程。讨论了控制生物硫气体产生的环境因素。阐述了含硫气体释放进入大气后的环境归趋