Do alternate bacterial indicators and pathogens increase after centrifuge dewatering of anaerobically digested biosolids?

The objectives of this research were to evaluate the potential for sudden increase and/or regrowth of alternative bacteria as either indicators or pathogens after dewatering of thermophilic and mesophilically digested biosolids. The results showed that, in general, for thermophilic processes, even when a statistically significant (p < 0.05) sudden increase and regrowth occurred for fecal coliforms, Escherichia coli, and Enterococci, it did not occur for Salmonella or Aeromonas. For the mesophilic process evaluated, sudden increase did not occur, but regrowth occurred for fecal coliforms, E. coli, Enterococci, and Salmonella. The results have implications for Class A and B biosolids regulations, as both fecal coliform and Salmonella are part of the regulatory limits. The results also suggest that the public health risks are minimal, as a result of the potential sudden increase and regrowth that may occur.     

离心机考核测试和带式机脱水性能试验研究

为配合吉林化学工业股份有限公司 30万t乙烯工程A/O工艺废水处理工程化学污泥脱水的需要 ,进行了生产运行离心机性能考核测试和小型带式压滤机应用于化学污泥脱水的中试性能试验研究。本研究确定了小型带式压滤机最佳投泥量、投药量和产泥量等指标。达到了验收的各项技术经济指标 ,具有显著的经济和环境效益。     

A comparison of membrane bioreactor and conventional-activated-sludge mixed liquor and biosolids characteristics.

Characteristics and behavior of raw and digested mixed liquor derived from a membrane bioreactor (MBR) and a full-scale activated-sludge (FSAS) facility were compared. The accumulation of nondegradable chemical oxygen demand in the MBR appears to play an important role in increasing the observed biological yield coefficient (Y(obs)), reducing average floc size, decreasing total suspended solids/total solids and volatile suspended solids/volatile solids (VS) ratios, and reducing specific-oxygen-uptake rates of the mixed liquor relative to FSAS-derived biological solids. Membrane bioreactor sludges exhibited lower VS destruction following 30 days mesophilic-anaerobic and aerobic digestion when compared to FSAS sludges. Significant deterioration in dewatering behavior was observed for the FSAS biosolids after anaerobic digestion and, to a lesser extent, following aerobic digestion. In comparison, digestion had a small affect on dewatering efficiency and conditioner requirements for MBR biosolids. Full-scale facilities using membrane separation may need to tailor digestion and dewatering processes to the specific characteristics of MBR sludges.     

Recurrence of fecal coliforms and Salmonella species in biosolids following thermophilic anaerobic digestion.

The U.S. Environmental Protection Agency (U.S. EPA) Part 503 Biosolids Rule requires the fecal coliform (indicator) or Salmonella species (pathogen) density requirements for Class A biosolids to be met at the last point of plant control (truck-loading facility and/or farm for land application). The three Southern Californian wastewater treatment plants in this study produced biosolids by thermophilic anaerobic digestion and all met the Class A limits for both fecal coliforms and Salmonella sp. in the digester outflow biosolids. At two plants, however, a recurrence of fecal coliforms was observed in postdigestion biosolids, which caused exceedance of the Class A limit for fecal coliforms at the truck-loading facility and farm for land application. Comparison of observations at the three plants and further laboratory tests indicated that the recurrence of fecal coliforms can possibly be related to the following combination of factors: (1) incomplete destruction of fecal coliforms during thermophilic anaerobic digestion, (2) contamination of Class A biosolids with fecal coliforms from external sources during postdigestion, (3) a large drop of the postdigestion biosolids temperature to below the maximum for fecal coliform growth, (4) an unknown effect of biosolids dewatering in centrifuges. At Hyperion Treatment Plant (City of Los Angeles, California), fecal coliform recurrence could be prevented by the following: (1) complete conversion to thermophilic operation to exclude contamination by mesophilically digested biosolids and (2) insulation and electrical heat-tracing of postdigestion train for maintaining a high biosolids temperature in postdigestion.     

Effect of biopolymer on the dewatering characteristics of autothermal thermophilic aerobic digestion of sludges.

Autothermal thermophilic aerobic digestion of sludge is known to produce poorly dewatering sludges. Laboratory studies were conducted to investigate the reasons for the poor dewatering. It was found that, during digestion, proteins and polysaccharides were released into solution, and that these could be linked to the deterioration in dewatering. The biopolymer release was accompanied by an increase in the monovalent-to-divalent (M/D) cation ratio. The degree to which the M/D caused deterioration of the sludges depended on the presence of iron in sludge. When the iron content was high, the release of protein and polysaccharides was low. When iron was low, the release of protein and polysaccharides increased linearly with the M/D ratio. The dose of conditioning chemicals, cationic polymer or ferric chloride, was related to the amount of colloidal biopolymer present in solution. The findings suggest that the addition of iron during the digestion process has the potential to produce better dewatering sludges.     

Impact of sewage sludge treatment processes on the removal of the endocrine disrupters nonylphenol ethoxylates

Several treatment processes of mixed sludge naturally contaminated with nonylphenol ethoxylates (NPE) were compared in order to evaluate their efficiency for the removal of these endocrine disrupters. Anaerobic and aerobic treatments were carried out in continuous stirred tank reactors, operated separately or combined together, at mesophilic and thermophilic temperatures and with or without ozone post-treatment. Anaerobic mesophilic removal of NPE consisted of complete removal of nonylphenol diethoxylate, incomplete removal of nonylphenol monoethoxylate and non stoechiometric production of nonylphenol, with consequently a NPE removal of 25%. At thermophilic temperature, anaerobic digestion led to an increase of the total solids removal efficiency, while improving NPE degradation (30%). Under thermophilic aerobic condition, the three compounds were removed simultaneously with a NPE removal efficiency higher than under anaerobic condition (39%). This removal is always well correlated to the total solids removal meaning that bioavailability remains the main limiting factor. Combination of either thermophilic aerobic-mesophilic anaerobic or mesophilic anaerobic-ozonation treatments enhanced the NPE removal by comparison to single systems (45% and 48%, respectively). These results confirm the high potential of existing and up-grading sewage sludge treatments to degrade such refractory and aged compounds.     

Regrowth of fecal coliforms in class A biosolids.

Eight types of Class A biosolids were tested for fecal coliform (FC) reactivation and/or regrowth at 20, 35, and 50 degrees C for 21 days. Growth of FC did not occur at 20 or 50 degrees C, but it was observed in two samples incubated at 35 degrees C after a lag period of 48 hours. In undigested biosolids, final FC concentration exceeded 10(4) MPN/g, whereas in thermophilically digested biosolids, the final FC concentration remained below 10(3) MPN/g, as FC regrowth may have been affected by the presence of the anaerobic bacterial consortium responsible for the digestion process. Fecal-coliform reactivation and regrowth within treatment plant operations seem unlikely but can occur in land application of biosolids.     

Laboratory-scale comparison of anaerobic-digestion alternatives.

Laboratory-scale digesters were used to perform side-by-side evaluations of alternative digestion systems including thermophilic-mesophilic-phased digestion (TPAD), acid/methane-phased digestion, mesophilic digestion, and the performance of the thermophilic stage of TPAD alone. Total detention times in the systems evaluated varied from 8 to 20 days. Temperatures in the mesophilic stage of TPAD were varied from 35 to 43.3 degrees C and temperatures in the thermophilic stage were varied from 55 to 58.9 degrees C. The purpose of the study was to evaluate volatile solids (VS) reduction and thickening properties of the different systems. Parameters evaluated included solids, volatile acids, gas production and quality, various chemical constituents of the sludge, and thickening properties using polymer and ferric chloride plus polymer. The TPAD systems were found capable of higher VS destruction at total detention times of 10 and 12.5 days compared to single-stage mesophilic or thermophilic digestion at 15 to 20 days. A laboratory-scale thickening test was performed to evaluate thickening properties. Based on obtaining 95% capture in the test, the polymer demand of mesophilic and acid-methane-phased digestion was the lowest. The TPAD system required approximately 180% of the dosage of the mesophilic sludge and thermophilic sludge required approximately 310% of the dosage. Temperatures of 40.5 and 43.3 degrees C in the mesophilic stage of TPAD were found to increase the polymer requirement and decrease the VS reduction of the TPAD system. Higher temperatures (above 56.1 degrees C) and lower detention times (less than 15 days) in the thermophilic digesters seemed to result in problems with degradation of volatile acids, particularly propionic acid.     

Anaerobic digestion of raw and thermally hydrolyzed wastewater solids under various operational conditions

In this study, high-solids anaerobic digestion of thermally pretreated wastewater solids (THD) was compared with conventional mesophilic anaerobic digestion (MAD). Operational conditions, such as pretreatment temperature (150 to 170 degrees C), solids retention time (15 to 20 days), and digestion temperature (37 to 42 degrees C), were varied for the seven THD systems operated. Volatile solids reduction (VSR) by THD ranged from 56 to 62%, compared with approximately 50% for MAD. Higher VSR contributed to 24 to 59% increased biogas production (m3/kg VSR-d) from THD relative to MAD. The high-solids conditions of the THD feed resulted in high total ammonia-nitrogen (proportional to solids loading) and total alkalinity concentrations in excess of 14 g/L as calcium carbonate (CaCO3). Increased pH in THD reactors caused 5 to 8 times more un-ionized ammonia to be present than in MAD, and this likely led to inhibition of aceticlastic methanogens, resulting in accumulation of residual volatile fatty acids between 2 and 6 g/L as acetic acid. The THD produced biosolids cake that possessed low organic sulfur-based biosolids odor and dewatered to between 33 and 39% total solids. Dual conditioning with cationic polymer and ferric chloride was shown to be an effective strategy for mitigating dissolved organic nitrogen and UV-quenching compounds in the return stream following centrifugal dewatering of THD biosolids.     

Influence of staging, mean cell residence time, and thermophilic temperature on the thermophilic anaerobic digestion process.

As Class B biosolids land application has become less acceptable to many local jurisdictions, low-cost processes to achieve Class A standards have become more popular. Prominent among these low-cost processes is thermophilic anaerobic digestion. As a result, thermophilic anaerobic digestion is now a popular topic in wastewater treatment literature, but quantifiable methods for selecting a particular thermophilic process have not been offered. To provide for this need, an empirical model was developed from data collected in thermophilic anaerobic digestion studies conducted using East Bay Municipal Utility District's (Oakland, California) primary and waste activated sludge to feed both bench- and full-scale digesters. The model predicts at which thermophilic temperature and mean cell residence time (MCRT) one process will outperform or equal another, with respect to fecal coliform reduction. The different disinfection efficiencies in the different thermophilic processes might be explained by the presence or absence of high volatile acid and/or un-ionized ammonia levels in the processes' digested sludges. Data from these studies also show an apparent relationship between increased thermophilic temperatures and volatile solids destruction, and between increased temperatures and specific volatile acids production, for digesters operating at a 13-day MCRT and higher, but not for digesters operating at a 2-day MCRT.     

Characteristics of biosolids in dimethyl ether dewatering method

In this study, a method for removing water from biosolids that uses dimethyl ether (DME) as an extractant was considered. This study evaluates the applicability of the DME dewatering method to biosolid cakes by using a DME flow-type experimental apparatus. It was found that a high dewatering ratio is clearly achieved by increasing the liquefied DME/biosolid ratio and lowering the liquefied DME linear velocity. As the liquefied DME/biosolid ratio was increased, the carbon content in dewatered biosolid showed a slight decrease and the TOC concentration in separated liquid increased significantly. Finally, the input energy Es to remove 1 kg of water from the biosolid cake, using both the DME dewatering method and the conventional drying method was estimated. The calculation shows that Es for the DME dewatering process is approximately a third of Es for the conventional thermal drying process.     

Generation pattern of sulfur containing gases from anaerobically digested sludge cakes.

Eleven dewatered sludge cakes collected from anaerobic digesters at different treatment plants were evaluated for the amount, type, and pattern of odorous gas production. All but one of the sludge cakes were from mesophilic anaerobic digesters. One was from a thermophilic digester. The pattern and quantities of sulfur gases were found to be unique for each of the samples with regard to the products produced, magnitude, and subsequent decline. The main odor-causing chemicals were volatile sulfur compounds, which included hydrogen sulfide, methanethiol, and dimethyl sulfide. Volatile sulfur compound production peaked in 3 to 8 days and then declined. The decline was a result of conversion of organic sulfur compounds to sulfide. In one side-by-side test, a high-solids centrifuge cake generated more odorous compounds than the low-solids centrifuge cake. The data show that anaerobic digestion does not eliminate the odor potential of anaerobically digested dewatered cakes.     

完全一体化结构的带式污泥浓缩压滤机

通过对带式浓缩压滤机设计和以往的工程实践,从机械结构设计角度分析和对比了完全一体化带式浓缩压滤机与传统意义上的(搭接式)带式浓缩压滤机结构特点,并且提供了完全一体化带式浓缩压滤机的设计参数。     

脱硫石膏粒径分布与脱水性能实验研究

脱硫石膏粒径分布是影响脱硫石膏浆液脱水性能的重要因素之一,以干法、湿法筛分和研磨破碎获得不同粒径分布的脱硫石膏,在相同的过滤条件下,对不同粒径分布脱硫石膏浆液脱水性能进行了研究,实验结果表明,当脱硫石膏粒径d50大于50μm且（d90-d10）小于100μm,真空过滤最大真空度不低于0．098MPa,过滤时间不少于2．5min,滤饼厚度不超过20mm时,石膏滤饼含水率可以降低到12％以下（最低可达10％）;d50在17μm为脱硫石膏在相同的过滤条件下能够实现真空脱水干燥的转折点;d50和（d90-d10）共同影响石膏脱水性能,d50小于20μm时,仅表现为d50的影响。     

Steam-explosion pretreatment for enhancing anaerobic digestion of municipal wastewater sludge.

This study evaluated the use of steam explosion as a pretreatment for municipal wastewater treatment sludges and biosolids as a technique for enhancing biogas generation during anaerobic digestion. Samples of dewatered anaerobic digester effluent (biosolids) and a mixture of thickened waste activated sludge (TWAS) and biosolids were steam-exploded under differing levels of intensity in this study. The results indicate that steam explosion can solublize components of these sludge streams. Increasing the intensity of the steam-explosion pressure and temperature resulted in increased solublization. The steam-explosion pretreatment also increased the bioavailability of sludge components under anaerobic digestion conditions. Increasing the steam-explosion intensity increased the ultimate yield of methane during anaerobic digestion. Batch anaerobic digestion tests suggested that pretreatment at 300 psi was the most optimal condition for enhanced biogas generation while minimizing energy input. Semicontinuous anaerobic digestion revealed that the results that were observed in the batch tests were sustainable in prolonged operation. Semicontinuous digestion of the TWAS/biosolids mixture that was pretreated at 300 psi generated approximately 50% more biogas than the controls. Semicontinuous digestion of the pretreated biosolids resulted in a 3-fold increase in biogas compared with the controls. Based on capillary suction test results, steam-explosion pretreatment at 300 psi improved the dewaterability of the final digested sludge by 32 and 45% for the TWAS/ biosolids mixture and biosolids, respectively, compared with controls. The energy requirements of the nonoptimized steam-explosion process were substantially higher than the additional energy produced from enhanced digestion of the pretreated sludge. Substantial improvements in energy efficiency will be required to make the process viable from an energy perspective.     

连续在线滤袋式淤泥脱水技术

以太湖淤泥为研究对象,研究了絮凝剂和滤袋性质对淤泥脱水性能的影响,并进行了滤袋脱水中试研究。结果表明,淤泥的含水率为90％时,在PAM和PAC最佳添加量55mg／L和1000mg／L条件下,淤泥比阻从8．7×10^7S2／g降低到2．0×10^7S2／g,Zeta电位从-28．77mV变成-4．68mV,滤袋平均过滤速度提高了137．9％,脱水性能显著提升。不同含水率下的实验得出了淤泥的最佳絮凝剂添加曲线;特殊材料滤袋相比于普通材料滤袋,滤袋的脱水综合能力大幅度提升,平均过滤速度达到0．479m^3／（m^2·h）,淤泥回收率为98．7％,泥饼含水率为71．6％;中试实验表明,淤泥经过4h过滤后,淤泥的含水率降到较低的65％,最终回收率可达到98．6％,滤液中污染物浓度满足国家排放标准。与传统技术相比,本技术具有脱水周期短、成本低、操作简单、安全性强等优点。     

A kinetic study of anaerobic digestion of olive mill wastewater at mesophilic and thermophilic temperatures

The kinetics of the anaerobic digestion of olive mill wastewater (OMW) was studied in the mesophilic and thermophilic ranges of temperature. Two completely mixed continuous flow bioreactors operating at 35 degrees C and 55 degrees C and with an average biomass concentration of 5.45 g VSS litre(-1) were used. The thermophilic reactor worked satisfactorily between hydraulic retention times (HRT) of 10 to 40 days, removing between 94.6 and 84.4% of the initial chemical oxygen demand (COD). In contrast, the mesophilic reactor showed a marked decrease in substrate utilization and methane production at a HRT of 10 days. TVFA levels and the TVFA/alkalinity ratio were higher and close to the suggested limits for digester failure. The yield coefficient for methane production (1 CH(4) STP g(-1) COD(added)) was 28% higher in the thermophilic process than in the mesophilic one. Macroenergetic parameters, calculated using Guiot's kinetic model, gave yield coefficients for the biomass (Y) of 0.18 (mesophilic) and 0.06 g VSS g(-1) COD (thermophilic) and specific rates of substrate uptake for cell maintenance (m) of 0.12 (mesophilic) and 0.27 g COD g(-1) VSS.day(-1) (thermophilic). The experimental results showed the rate of substrate uptake (R(s); g COD g(-1) VSS.day(-1)), correlated with the concentration of biodegradable substrate (S(b); g COD litre(-1)), through an equation of the Michaelis-Menten type for the two temperatures used.     

Laboratory evaluation of thermophilic-anaerobic digestion to produce Class A biosolids. 1. Stabilization performance of a continuous-flow reactor at low residence time.

There is increasing interest in the United States in producing biosolids from municipal wastewater treatment that meet the criteria for Class A designation established by the U.S. Environmental Protection Agency. Class A biosolids are intended to be free of pathogens and also must meet requirements for reduction of the vector-attraction potential associated with untreated sludge. High-temperature processes are considered to produce Class A biosolids if the combination of operating temperature and treatment time exceeds minimum criteria, but this option is not applicable to mixed, continuous-flow reactors. Such reactors, or any combination of reactors that does not meet the holding time requirement at a specific temperature, must be demonstrated to inactivate pathogens to levels consistent with the Class A criteria. This study was designed to evaluate pathogen inactivation by thermophilic anaerobic digestion in a mixed, continuous-flow reactor followed by batch or plug-flow treatment. In this first of a two-part series, we describe the performance of a continuous-flow laboratory reactor with respect to physical and chemical operating parameters; microbial inactivation in the combined continuous-flow and batch treatment system is described in the second part. Sludges from three different sources were treated at 53 degrees C, while sludge from one of the sources was also treated at 55 and 51 degrees C. Relatively short hydraulic retention times (four to six days) were used to represent a conservative operating condition with respect to pathogen inactivation. Treatment of a fermented primary sludge led to an average volatile-solids (VS) destruction efficiency of 45%, while VS destruction for the other two sources was near or below 38%, the Class A criterion for vector attraction reduction. Consistent with other studies on thermophilic anaerobic digestion of sludges at short residence times, effluent concentrations of volatile fatty acids (VFAs) were relatively high. Also consistent with other studies, the most abundant VFA in the effluent was propionate. Gas production ranged from 0.3 to 0.5 m3/kg VS fed and from 0.8 to 1.3 m3/kg VS destroyed.     

Utilization of urban sewage sludge: Chinese perspectives

Purpose

Urbanization and industrialization in China has resulted in a dramatic increase in the volume of wastewater and sewage sludge produced from wastewater treatment plants. Problems associated with sewage sludge have attracted increasing attention from the public and urban planners. How to manage sludge in an economically and environmentally acceptable manner is one of the critical issues that modern societies are facing.

Methods

Sludge treatment systems consist of thickening, dewatering, and several different alternative main treatments (anaerobic digestion, aerobic digestion, drying, composting, and incineration). Agricultural application, landfill, and incineration are the principal disposal methods for sewage sludge in China. However, sewage sludge disposal in the future should focus on resource recovery, reducing environmental impacts and saving economic costs.

Results

The reuse of biosolids in all scenarios can be environmentally beneficial and cost-effective. Anaerobic digestion followed by land application is the preferable options due to low economic and energy costs and material reuse.

Conclusion

It is necessary to formulate a standard suitable for the utilization of sewage sludge in China.     

Overview of anaerobic treatment: thermophilic and propionate implications.

Difficulties in achieving low propionate concentrations in anaerobically treated effluents are frequently reported in the literature (Ahring, 1994; Kugelman and Guida, 1989; Rimkus et al., 1982), especially at thermophilic temperatures, with concentrations as high as 1000 to 9600 mg/L sometimes produced. This paper will detail the effect of several variables on the performance of both mesophilic and thermophilic regimes. Studies concerning the effect of the following four important factors on performance are included: reactor configuration, inorganic nutrient supplementation, substrate characteristics, and the unique role of microbial consortia proximity in enhancing performance. Reactor configuration modifications, essential nutrient additions, and the importance of close microbial proximity were all found to contribute to improvement in thermophilic anaerobic digestion in all the studies. It was found that, in substrates that shunt significant amounts of the electron donor through propionate, performance was critically related to reactor optimization, with propionate removal efficiency considerably improved using intact upflow anaerobic sludge blanket granules, less so in a homogenized granule slurry blanket, and noticeably reduced even more when the completely stirred reactor configuration of homogenized granules was used. The critical importance of extremely close microbial consortia proximity in maintaining hydrogen intermediates at very low levels to efficiently convert propionate to hydrogen and acetate was demonstrated. Compared to mesophilic digestion, thermophilic digestion manifested elevated levels of propionate, except in the nonmixed reactors, which had close microbial consortia proximity. The reactor configuration with the best results was the anaerobic digestion elutriated phased treatment (ADEPT) scheme, in which the raw sludge was elutriated of its fermenting volatile fatty acids, as they are generated in a short 5- to 8-day solids retention time (SRT) in one reactor and the elutriate then metabolized by passing up through a methanogenic granule or slurry blanket (with its close microbial consortia proximity) in a separate reactor with a 20- to 50-day SRT. Loading rates and performance of the ADEPT reactor configuration were superior to the standard continuously stirred tank reactor, and ADEPT thermophilic temperatures allowed higher organic loading rates without high propionate concentrations in the effluent.