Aerobic Thermophilic and Anaerobic Mesophilic Treatment of Sludge

The objective of this research was to investigate the effectiveness of aerobic thermophilic treatment in enhancing conventional anaerobic mesophilic digestion in terms of pathogen reduction. vector attraction reduction, volatile solids (VS) reduction, gas production, and product sludge dewaterability. Lab-scale two-stage experiments were conducted with the aerobic thermophilic stage as pretreatment (AerTAnM) or as posttreatment (AnMAerT) to mesophilic anaerobic digestion. The lab-scale AerTAnM and AnMAerT systems were operated at system sludge residence times (SRTs) of 15 and 15.5 days, thermophilic reactor temperature = 62°C, and mesophilic reactor temperature = 37°C. The control anaerobic digester was operated at a system SRT of 15 and 15.5 days and temperature = 37°C. The AerTAnM and AnMAerT systems and control anaerobic digester operated at a system SRT of 15 days were able to achieve VS reductions of >38% (Class A sludge vector attraction reduction requirement). The VS reductions by the AerTAnM and AnMAerT systems (～65%) were higher than the VS reduction in the control (～51%) by 14%. The AerTAnM and AnMAerT systems reduced fecal coliform density in the feed sludge from 108 most probable number (MPN) per gram of total solids (TS) to <103 MPN∕g TS (Class A sludge fecal coliform density limit), whereas the control reduced the same feed sludge fecal coliform density to about 106 MPN∕g TS. The AerTAnM and AnMAerT systems and control can reduce Salmonella density in the feed sludge from 5 to 12 MPN∕4 g TS to <1 MPN∕4 g TS. Average methane gas production by the AerTAnM system anaerobic mesophilic digester (0.61 m3∕kg VS destroyed) was higher than those of the AnMAerT system (0.50 m3∕kg VS destroyed) and control (0.52 m3∕kg VS destroyed) anaerobic mesophilic digesters. Average H2S content of the AerTAnM [133 ppm volume-to-volume ratio (v∕v)] system anaerobic thermophilic digester gas was significantly lower than those in gas from the AnMAerT system (249 ppm v∕v) and control (269 ppm v∕v) anaerobic mesophilic digesters. The dewaterabilities of the product sludge (measured as time-to-filter, s) from the AerTAnM system (237 s) and AnMAerT system (203 s) were significantly better than that of the product sludge from the control (346 s).     

Improved Anaerobic Process Efficiency Using Mesophilic and Thermophilic Elutriated Phased Treatment

An innovative anaerobic digestion elutriated phased treatment (ADEPT) has been evaluated at mesophilic (M-ADEPT) (35°C) and thermophilic (T-ADEPT) (55°C) temperatures in which the organic loading rate (OLR) was increased until reactor failure (pH<5.5). Single-stage continuously stirred tank reactors (CSTRs) at both temperatures were also operated as controls (M-CSTR for 35°C and T-CSTR for 55°C). The T-CSTR failed at an OLR of 7.4 g volatile solid (VS)/L?day and the M-CSTR at an OLR of 10 g VS/L?day while the M-ADEPT continued until an OLR of 18 g VS/L?day and the T-ADEPT reached an OLR of 24 g VS/L?day before system failure. The T-CSTR produced the poorest effluent quality as manifested by high propionate concentrations (1,500–2,500 mg/L) while both M-ADEPT and T-ADEPT produced much better quality of effluent with propionate concentrations below 100 mg/L. Thus it appears that the T-ADEPT design may solve effluent quality problems associated with normally high propionate concentrations produced during thermophilic anaerobic digestion. Superior effluent quality, reduced reactor volume requirements, more stable methanogenesis due to the extended solids retention time, and uncoupling of the methanogen wasting from the refractory sludge wasting process resulted in stable and efficient processing at both temperatures for the innovative ADEPT design. Because the higher amounts of volatile fatty acids produced in the acid elutriation phase of the ADEPT system can be a favorable carbon source for biological nutrient removal in wastewater treatment plants, this positive aspect should be considered in future applications of the ADEPT system.     

Metal Stimulation and Municipal Digester Thermophilic/Mesophilic Activity

Biomass from thermophilic and mesophilic digesters (four temperature-phased anaerobic digesters and one phased thermophilic digester) was assayed for potential methane production rate increases resulting from nutrient (Ni, Co, and Fe) addition. Furthermore, digester operations and biomass activities were compared. The majority (77%) of biomass samples benefited from nutrients, with propionate and acetate utilization rates increasing as much as 50 and 35%, respectively, after nutrient addition. Propionate utilization rates were more frequently stimulated by nutrient addition, demonstrating increased methane production rates of from 14 to 50% upon nutrient amendment. Others have observed difficulty achieving low propionate concentrations in municipal thermophilic digesters, especially at lower retention times. Trace nutrient supplementation is one method to increase propionate and acetate utilization in some municipal thermophilic as well as mesophilic digesters.     

Temperature and SRT Effects on Aerobic Thermophilic Sludge Treatment

Laboratory-scale experiments were conducted to determine optimum sludge residence time (SRT) and temperature of aerobic thermophilic pretreatment (ATP) of mixed sludge (thickened waste activated sludge and primary sludge) to achieve maximum pathogen reduction and best process performance. 4-L laboratory-scale ATP reactors were operated at SRTs of 0.6, 1.0, and 1.5 days and temperatures of 55, 58, 62, and 65°C. ATP at temperatures ≥62°C and SRT ≥0.6 day reduced the feed sludge fecal coliform density from 107 MPN∕g total solids (TS) to <104 MPN∕g TS. Salmonella in the feed sludge was reduced to <1 MPN∕4 g TS from 2 to 18 MPN∕4 g TS by ATP at temperatures ≥55°C and SRT ≥0.6 day. ATP was able to increase sludge volatile acids concentration by 100–200% over the feed sludge volatile acid concentration and to reduce sludge supernatant chemical oxygen demand from 20,000 to 22,000 mg∕L in the feed to 13,000–17,000 mg∕L in the ATP reactor. Volatile solids reduction by ATP increased from 25 to 40% when SRT was increased from 0.6 to 1.5 days, and a 5% increase in volatile solids reduction was seen at SRTs of 0.6, 1.0, and 1.5 days when ATP temperature was increased from 55 to 65°C.     

Enhancement of Anaerobic Digestion of Excess Municipal Sludge with Thermal and/or Oxidative Treatment

The use of thermal and/or oxidative treatment to enhance anaerobic digestion of excess municipal sludge was evaluated. Different reactor configurations were studied. A “moderate” temperature (90°C) was used in the thermal treatment and hydrogen peroxide was the oxidant. Thermal treatment alone did not increase solids destruction. A maximum of 15.2% increase in volatile suspended solids (VSS) destruction was observed with the oxidative treatment. A synergistic effect was observed when both treatments were combined. The increase in VSS destruction when both cotreatments were applied (oxidative and thermal) ranged between 27.2 and 29.0%, depending on the reactors configuration. Parameters such as methane production, chemical oxygen demand removal, nitrogen and volatile fatty acids concentrations, and fecal coliforms removal were also evaluated for the different configurations studied.     

Multistaged Anaerobic Sludge Digestion Processes

Two multistaged anaerobic digestion systems, a four-stage thermophilic anaerobic digestion (4TAD), all at 55°C, and a four-stage anaerobic digestion with a tapered temperature configuration (4ADT) at 55, 49, 43, and 37°C, respectively, were studied to evaluate their solids, volatile organic sulfur compounds, and indicator organism (E. coli and fecal coliform) reduction potentials. The 4TAD system removed significantly more volatile solids from sludges than the 4ADT system (6%). However, the dewatered biosolids cakes from the 4ADT system generated fewer organic sulfur compounds than those from the 4TAD system. Both multistage systems showed better digestion efficiencies than single-stage mesophilic or single-stage thermophilic anaerobic digesters at the same overall retention time. However, the lowest organic sulfur compounds were observed from the single mesophilic system. Both multistage anaerobic digestion systems failed to dramatically remove DNA of the indicator organism, E. coli, quantified by real time polymerase chain reaction, even though the indicator organism densities measured by standard culturing methods satisfied EPA Class A biosolids requirements.     

Utilization of an Activated Sludge for the Improvement of an Existing Thermophilic Wastewater Treatment System

A pilot-scale activated sludge system was started to determine its effectiveness in treating the thermophilic biological effluent from an existing organic chemical industrial wastewater treatment system. Preliminary results demonstrated that an additional 95% biological oxygen demand and 65% dissolved organic carbon removal was achieved. In addition, significant biodegradation of the volatile organic compounds and organic nitrogen was observed.     

Examination on Process Configurations Incorporating Thermal Treatment for Anaerobic Digestion of Sewage Sludge

This study aimed to examine the process configurations for mesophilic anaerobic digestion of sewage sludge, when incorporated with thermal treatment of 120°C for 1?h. Four types of process configurations were designed: control (no thermal treatment), pretreatment and posttreatment configurations of the single-stage process, and an interstage-treatment configuration of the two-stage process. The lab-scale digesters were operated at 35°C with the sewage sludge of 4.5% total solids, and were equally set at the total hydraulic retention time of 20 days. At the steady state, the control digester showed 35.3% of volatile solids (VS) destruction and 0.168?L/g VS fed of methane production. Compared to the control, the VS destruction in the pre-, post-, and interstage-treatment configurations was increased by 4.5, 6.6, and 9.9%, respectively, while the methane production in the post- and interstage-treatment configurations was improved by 0.036 and 0.028?L/g VS fed, respectively. The pretreatment configuration yielded identical methane production to the control. Therefore, it is more effective on anaerobic digestibility to apply the moderate thermal treatment after sewage sludge is digested once. On the other hand, the increase in soluble chemical oxygen demand and deterioration of dewaterability were observed, when solids destruction was improved.     

Anaerobic Biodegradation of Polyhydroxybutyrate in Municipal Sewage Sludge

Anaerobic biodegradation in sewage sludge of polyhydroxybutyrate (PHB) was investigated. Evolved gaseous carbon was measured to assess biodegradability according to ASTM D5210. Mass-loss experiments were performed to determine degradation kinetics. Changes in the polymer properties were investigated. The impact of a natural plasticizer [tributyl citrate (TBC)] on biodegradation was determined. Polylactic acid was also biodegraded for comparison. Melt-pressed plates of PHB (with thicknesses of 0.24, 0.5, 1.2, 3.5, and 5.0 mm) were biodegraded to investigate the relationship between initial mass:initial surface area ratios and decay rates. Scanning electron microscopy micrographs of degraded specimens were recorded for visual illustration of the degradation process. A relationship between initial mass:initial surface area and degradation rates indicates that the thickness and surface area of the material affect its degradation. The degradation rates were impacted by the sewage sludge activity. TBC additive hindered PHB’s rate of degradation. Thermal properties, molecular bonding, and molecular weight measured by differential scanning calorimetry, Fourier transform infrared, and size exclusion chromatography, respectively, were only slightly affected by biodegradation, indicating that recycling PHB will not affect its performance.     

内循环厌氧反应器厌氧颗粒污泥的特性研究

厌氧颗粒污泥是厌氧反应器高效稳定运行的基础和关键。试验研究利用了一种改进型的内循环厌氧反应器,克服了传统内循环厌氧反应器结构复杂易引起堵塞等缺点,对厌氧颗粒污泥的特性进行研究,研究厌氧颗粒污泥的特性对生产实践具有重要的指导意义。该试验研究是在改进型内循环厌氧反应器稳定运行的基础上,对颗粒污泥的粒径分布、污泥产甲烷活性、DGGE等特性进行分析。     

厌氧消化污泥稳定化评价指标综述

对污泥稳定的定义及目标进行了介绍，并对评价厌氧污泥稳定度的参数指标进行了综述。推荐的几个测试是：挥发性固体减少率、不稳定物质减少测试、腐殖质含量、植物毒性测试，指出应从两个方面来考虑对参数进行选择，需要掌握稳定化过程的信息量和最终资源化利用的方式。     

厌氧消化污泥稳定化评价指标综述

对污泥稳定的定义及目标进行了介绍,并对评价厌氧污泥稳定度的参数指标进行了综述,推荐的几个测试是:挥发性固体减少率、不稳定物质减少测试、腐殖质含量、植物毒性测试,指出应从两个方面来考虑对参数进行选择,需要掌握稳定化过程的信息量和最终资源化利用的方式。     

Low-Strength Wastewater Treatment with Combined Granular Anaerobic and Suspended Aerobic Cultures in Upflow Sludge Blanket Reactors

Combined cultures were developed from anaerobic granular and suspended aerobic cultures in three upflow sludge blanket reactors aerated at 10?mL air/min 4?h/day (R2), every other day (R3), and 24?h/day (R4). The use of combined cultures was found to be advantageous compared to the anaerobic granules for the treatment of low-strength wastewaters. During municipal wastewater treatment at influent 5-day biochemical oxygen demand (BOD5) concentration of 53–118?mg/L (hydraulic retention time: 0.75?day), combined cultures in R2, R3, and R4 exhibited average BOD5 removal efficiencies of 52, 75, and 76%, respectively. The use of these cultures might be proposed as an alternative for municipal wastewater treatment due to their advantages such as achievement of required discharge standards, prevention of biomass loss/settleability problems unlike activated sludge systems and possible methanogenic activity, as well as high settling characteristics comparable to those of anaerobic granules.     

Biotransformation of Carbon Tetrachloride and Anaerobic Granulation in a Upflow Anaerobic Sludge Blanket Reactor

Carbon tetrachloride (CT) in a synthetic wastewater was effectively degraded in a 2?l upflow anaerobic sludge blanket reactor during the granulation process by increasing the chemical oxygen demand (COD) and CT loadings. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to mass (F/M) ratio, and specific methanogenic activity (SMA) were also detected during granulation. Over 97% of CT was removed at 37°C, at a COD loading rate of 10?g/L?day. Chemical oxygen demand and CT removal efficiencies of 92 and 88% were achieved when the reactor was operating at CT and COD loading rates of 17.5?mg/L?day and 12.5?g/L?day, respectively. This corresponds to an hydraulic retention time of 0.28?day and an F/M ratio of 0.57?g?COD/g?volatile?suspended?solids?(VSS)?day. In 4?weeks, the seed sludge developed the CT degrading capability that was not very sensitive to shocks. The granular sludge cultivated had a maximum diameter of 2.5?mm and SMA of 1.64?g?COD/g?VSS?day. Glucose biodegradation by CT acclimated anaerobic granules was expressed with competitive inhibition. However the competitive inhibition was not significant since the competitive inhibition coefficient (Ki) was as high as 18.72?mg/L. Kinetic coefficients of k (maximum specific substrate utilization rate), Ks (half velocity coefficient), Y (growth yield coefficient), and b (decay coefficient) were determined as 0.6/day, 1.1?mg/L, 0.23?g?VSS/g glucose-COD, and 0.01/day, respectively, based on growth substrate glucose–COD during CT biotransformation. The CT was treated via biodegradation and this contributed to 89% of the total removal. The removal contributions from biomass adsorption, abiotic transformation, and volatilization were negligible. Adsorption and volatilization accounted for only 0.8 and 0.5% of the total removal, respectively.     

Biohydrogen Production by Mesophilic Anaerobic Fermentation of Glucose in the Presence of Linoleic Acid

In this work, linoleic acid (LA), a long chain fatty acid bearing 18 carbons and two double bonds, inhibited hydrogen consumption in a mixed anaerobic culture acclimated to glucose. At pH = 7.6, a metabolic shift from methane to hydrogen formation was observed in cultures maintained at 37°C and fed 5,000?mg?L?1 glucose in the presence of 500–2,000?mg?L?1 LA. The hydrogen yield increased with increasing LA levels while the quantity of methane decreased. The major volatile fatty acids produced were acetate and butyrate with greater levels observed in cultures fed with LA. Acetate, butyrate, and hydrogen accumulation suggests inhibition of aceticlastic methanogens, hydrogenotrophic methanogens, and butyrate degrading microorganisms, respectively, in the presence of LA. A maximum hydrogen yield of 1.71±0.22?mole?mole?1 glucose was observed only when glucose was reinjected into cultures receiving 2,000?mg?L?1 LA plus 5,000?mg?L?1 glucose.     

Determining the Volatile Fatty Acid Equivalent in Thermophilic Aerobically Digested Sludge Supernatant

Thermophilic aerobically digested (TAD) sludge supernatant has been found to be a potential carbon alternative for biological nutrient removal (BNR) enhancement in wastewater treatment plants. Carbonaceous substrates, other than the volatile fatty acids (VFAs) in TAD supernatant, were also found to be utilizable in BNR enhancement; however, these carbon compounds could not be detected by conventional chemical analyses (e.g., gas chromatography). A headspace carbon dioxide (CO2) monitoring method was tested in this study to estimate the overall available carbon source, or the VFAs accumulated in a microaerated TAD operation. This on-line method uses real activated sludge and TAD supernatant samples to determine the available carbon equivalent in real time. In comparison to the gas chromatography (GC) analyses of the TAD supernatant samples, the headspace CO2 monitoring method resulted in “overestimation” of VFA concentrations, in both the phosphorus release and denitrification reactions. Operating results suggested that the CO2 monitoring approach was capable of revealing the overall VFA equivalent that could be available for the main BNR reactions.     

Thermophilic Aerobic Wastewater Treatment in Continuous-Flow Bioreactors

Thermophilic aerobic biological wastewater treatment was investigated at 55°C in continuous-flow bioreactors using a synthetic wastewater containing gelatin and α-lactose as principal organic constituents. By operating multiple continuous-flow bioreactors at different hydraulic residence times (HRTs), the maintenance constant (kd) was calculated to be 0.046 day?1, a value approximately 10-fold lower than that previously reported for thermophilic processes but similar to that for mesophilic treatment. Investigation into the bacterial community structure by denaturing gradient gel electrophoresis of polymerase chain reaction-amplified 16S ribosomal RNA genes revealed that the dominant phylotypes in the bioreactors changed as a function of HRT. Cell reactivity, measured as the specific content of protein and RNA, declined as HRT increased. Catabolic enzyme activities specific to the principal organics in the synthetic wastewater, however, increased at higher HRTs. In conclusion, the performance of thermophilic aerobic biological wastewater treatment processes was similar to that of conventional mesophilic processes with respect to maintenance requirements (i.e., cell yields) as well as bacterial community shifts, cell reactivity, and cell activity.     

Minimization of Short-Circuiting Flow through Upflow Anaerobic Sludge Blanket Reactor

Performance data of upflow anaerobic sludge blanket (UASB) reactors treating different types of wastewater have been analyzed. A completely stirred tank reactor (CSTR) model with bypass flow was considered for evaluation of the behavior of sludge bed as well as the whole reactor. It demonstrated that the sludge bed in a UASB reactor behaves as a completely stirred tank reactor with bypass flow. The reactor performance has been shown to depend on the short-circuiting flow through the sludge bed. However, the short-circuiting flow depends on design and operational conditions of the reactor. To find out the relationships of various parameters with short-circuiting flow through the sludge bed, dimensional analysis was carried out. Principal component analysis was carried out by taking short-circuiting flow, concentration of the influent, superficial gas velocity, height of the sludge bed, concentration of the biomass in the sludge bed, and flow rate of the influent into consideration. Analysis reveals the relative importance of the parameters on the short-circuiting flow.