Anaerobic Filter Treatment of Municipal Wastewater: Biosolids Behavior

Three 12.5?L upflow anaerobic filter (AF) reactors, with ceramic saddle, plastic ring, and crushed stone packing, were employed to evaluate the treatment of raw municipal wastewater under a wide range of hydraulic and organic loadings and operating conditions. Emphasis is placed in this paper on column profile sampling, draining, and biomass evaluation studies conducted to ascertain the functioning of the reactors and accumulation of biosolids. The concentration of organics and solids within the AF gradually increased, starting at the low end and progressing to higher elevations. The peak chemical oxygen demand value measured within the reactors was 11,500?mg/L and was noted in the stone-packed unit at 20?cm after 1,009?days, and the stabilization of suspended material was greater in lower column sections. Packing material morphology influenced the removal by draining of entrapped biomass, and the volume of drainage recovered was substantially smaller than available void space. Biosolids retained in the saddle-packed unit after 34?months totaled 33?kg/1,000?m3 wastewater treated, and no signs of clogging were observed in any of the reactors.     

Toward Polyhydroxyalkanoate Production Concurrent with Municipal Wastewater Treatment in a Sequencing Batch Reactor System

Bacteria can synthesize cytoplasmic granules known as polyhydroxyalkanoates (PHAs), which are carbon and energy storage reserves, from organic carbon when subject to stressful environmental conditions. PHAs are also biodegradable thermoplastics with many potential commercial applications. The purpose of the research reported herein was to evaluate the feasibility of integrating PHA production within a municipal wastewater treatment (WWT) configured as a sequencing batch reactor (SBR). Four bench-scale WWT SBRs were tested at decreasing organic loading rates to assess the potential to enrich for microbes capable of feast/famine PHA synthesis. For each treatment SBR, sidestream batch reactors receiving higher quantities of primary solids fermenter liquor were operated to produce PHA. Results from this study demonstrate that a treatment SBR supplied moderate strength wastewater can enrich for the target microorganisms, with PHA yields of 0.23–0.31-mg PHA per mg chemical oxygen demand, and produce high quality effluent. In sidestream batch reactors, microorganisms that fed excess quantities of substrate can rapidly synthesize significant quantities of PHA. Based on the results of this study, we estimate that a 1 million gallon per day SBR WWT-PHA production system could generate 11–36 t (12–40 t) of PHA annually.     

Combined Anaerobic/Aerobic Secondary Municipal Wastewater Treatment: Pilot-Plant Demonstration of the UASB/Aerobic Solids Contact System

Anaerobic pretreatment followed by aerobic posttreatment of municipal wastewater is being used more frequently. Recent investigations in this field using an anaerobic fluidized bed reactor/aerobic solids contact combination demonstrated the technical feasibility of this process. The investigation presented herein describes the use of a combined upflow anaerobic sludge bed (UASB)/aerobic solids contact system for the treatment of municipal wastewater and attempts to demonstrate the technical feasibility of using the UASB process as both a pretreatment unit and a waste activated sludge digestion system. The results indicate that the UASB reactor has a total chemical oxygen demand removal efficiency of 34%, and a total suspended solids removal efficiency of about 36%. Of the solids removed by the unit, 33% were degraded by the action of microorganisms, and 4.6% accumulated in the reactor. This low solids accumulation rate allowed operating the UASB reactor for three months without sludge wasting. The long solids retention time in this unit is comparable to the one normally used in conventional sludge digestion units, thus allowing the stabilization of the waste activated sludge returned to the UASB reactor. Particle flocculation was very poor in the UASB reactor, and therefore, it required postaeration periods of at least 100?min to proceed successfully in the aerobic unit. Polymer generation, which is necessary for efficient biological flocculation, was practically nonexistent in the anaerobic unit; therefore, it was necessary to maintain dissolved oxygen levels greater than 1.5?mg/L in the aerobic solids contact chamber for polymer generation to proceed at optimum levels. Once these conditions were attained, the quality of the settled solids contact chamber effluent always met the 30?mg BOD/L, 30?mg SS/L secondary effluent guidelines.     

Membrane Fouling in Membrane Bioreactors for Wastewater Treatment

Membrane bioreactors (MBRs), in which membranes are applied to biological wastewater treatment for biomass separation, provide many advantages over conventional treatment. However, membrane fouling in MBRs restricts their widespread application because it reduces productivity and increases maintenance and operating costs. Recently much research and development has taken place to investigate, model, and control membrane fouling processes. However, unified and well-structured theories on membrane fouling are not currently available because of the complexity of the biomass matrix, which is highly heterogeneous and includes living microorganisms. Membrane fouling in MBR systems can be reversible (i.e., removable by physical washing) or irreversible (removable by chemical cleaning only), and can take place on the membrane surface or into the membrane pores. Although establishing a general model to describe membrane fouling in such a process is made extremely difficult by the inherent heterogeneity of the system, the nature and extent of fouling in MBRs is strongly influenced by three factors: biomass characteristics, operating conditions, and membrane characteristics. Fouling control techniques which have been investigated include low-flux operation, high-shear slug flow aeration in submerged configuration, periodical air or permeate backflushing, intermittent suction operation or addition of powdered activated carbon (PAC). Of these, only PAC addition is currently not used in existing large-scale installations.     

Comparison of Municipal and Coke Wastewater Sludges in Disintegration and Acidogenesis by Microwave

This work experimentally determined the effect of microwave treatment on the disintegration and acidogenesis of waste-activated sludges (WAS) from municipal and coke wastewater treatment plants. Sludge samples (500?g) were heated for 0, 3, 5, 7, 9, 11, and 15?min in a microwave oven (2,450?MHz, 700?W). The degree of sludge solubilization [soluble chemical oxygen demand (SCOD)/COD] increased asymptotically with microwave irradiation time from 1.5% at 0?min to 22.3% at 15?min for WAS from a municipal wastewater treatment plant (WASM) and 1.5% to 5.1% for WAS from a coke wastewater treatment plant of a steel manufacturing industry (WASC). The calcium concentrations in both sludges also increased with microwave irradiation time. The biochemical acidogenic potentials (BAP) increased from 3.70 to 4.44??g?COD?L-1 for WASM and 1.19 to 1.67??g?COD?L-1 for WASC. The results show that microwave irradiation increases the solubilization and BAP of sludges and that WASM had a higher degree of solubilization and BAP than WASC.     

Experimental Determination of Energy Content of Unknown Organics in Municipal Wastewater Streams

A bomb calorimetry method has been used for the first time to measure the energy content of raw municipal wastewater. The method was first validated using standard compounds (arginine, glucose, and propionic acid) and then tested with municipal sludge samples, with the results compared to previously published values. By drying a large enough sample to yield approximately 0.5 g of solid residue and using benzoic acid in a 1:1 ratio as a combustion aid, an accurate and precise measurement of the energy content of raw municipal wastewater can be made. The energy content measurements indicate that for the full-scale treatment facility examined, the potential energy available in the raw waste-water exceeds the electricity requirements of the treatment process by a factor of 9.3.     

Effect of Hexavalent Chromium on Performance of Membrane Bioreactor in Wastewater Treatment

The presence of toxic hexavalent chromium poses a great challenge in biological wastewater treatment. In this study, the performance of a membrane bioreactor (MBR) for the treatment of synthetic domestic wastewater in the presence of chromium was investigated. The carbonaceous pollutant removal is not affected by Cr(VI) with concentration ranging from 0.4 to 10 mg/L; it becomes slightly lower when the Cr(VI) is 50 mg/L. The nitrification efficiency of above 99% can be achieved when the waste stream is free of the metal or contains 0.4 mg/L chromium. When its concentration is 10 mg/L, nitrification efficiency above 50% is found; however, it becomes deteriorated in the presence of 50 mg/L chromium. The positive biomass growth, though lower than conventional activated sludge process, can be achieved at Cr(VI) concentration less than 10 mg/L; a decline in the cell growth occurs when the metal concentration is increased to 50 mg/L. Significant accumulation for the metal is observed when its concentration is 0.4 mg/L; however, almost no metal removal is observed when the concentration is above 10 mg/L. During eight-month continuous operation, the presence of Cr(VI) has an insignificant effect on the flux. The nitrifiers in the MBR are more sensitive to the presence of Cr(VI) than heterotrophs.     

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.     

Simultaneous Organic and Nutrient Removal in a Naturally Ventilated Biotower Treating Presettled Municipal Wastewater

The performance of a down-flow hanging sponge (DHS) system was continuously evaluated for 1 year for enhancement of organic matter and nutrient removal in the treatment of presettled municipal wastewater. A pilot-scale DHS (24 L) was installed at a wastewater-treatment site and operated at an ambient temperature of 25°C. This paper reports on the results of a long-term monitoring of the system. The DHS system was operated at three different hydraulic retention times (HRTs), i.e., 6, 4, and 2 h. The available results showed that increasing the HRT significantly improved the removal of chemical oxygen demand (COD) fractions. The removal efficiencies of COD were 89, 80, and 56% at HRTs of 6, 4, and 2 h, respectively. Also, ammonia (NH4–N) concentration significantly decreased by increasing the HRT. Ammonia removal percentages of 99, 90, and 72% were achieved when the DHS system was operated at HRTs of 6, 4, and 2 h, respectively, but decreasing HRT exerted a slightly negative effect on the removal of total phosphorous. Scanning electron microscopy observation revealed no clogging of the sponge pores after 12 months of continuous operation. Accordingly, the results suggested that the proposed system may be a competitive solution for municipal wastewater treatment under variable conditions.     

Lagoon Effluent Treatment Using Grass Filtration

The Western Treatment Plant (WTP) is one of the largest treatment plants in Australia treating more than 500 ML of sewage per day, discharging treated effluent to Port Phillip Bay in Victoria, Australia. The Port Phillip Bay Environmental Study (1992–1996) concluded that there was a need to reduce nitrogen loads from WTP to lower the risk of eutrophication, especially during winter when grass filtration was in operation. Therefore, in 1997, Melbourne Water initiated a pilot study to investigate the effectiveness of grass filtration for polishing wastewater that had received prior lagoon treatment. The study involved field monitoring of seven trial grass filtration bays at the WTP for hydraulic and water quality data from mid-May to early-October 1997. The results of the pilot study revealed that the removal rates of these nutrients were higher during the first half of the trials than during the second half. The results also showed that the removal rates of nutrients were inversely proportional to the hydraulic loading rates of the bays. A hydraulic loading rate of 40 mm/d was found to be optimal in this pilot study for achieving a balance between wastewater throughput and nutrient removal.     

Application of Cross-Flow Microfiltration for the Treatment of Combined Sewer Overflow Wastewater

Application of cross-flow microfiltration with and without backpulsing is evaluated for the treatment of dilute primary sewage effluent simulating combined sewer overflow wastewater. Four alpha alumina ceramic membranes of various pores sizes (0.2–5.0?μm) were tested to understand the impact of cross-flow velocity and transmembrane pressure on the permeate water quality and flux rate. The 0.2 and 0.8?μm membranes produced a permeate water quality that is likely to be suitable for surface water discharge. The combination of permeate chemical and biological water quality and long-term flux rates suggest that a 0.2?μm membrane would be the most appropriate membrane for the treatment of combined sewer overflow wastewater within sewersheds.     

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.     

Process Limits of Municipal Wastewater Treatment with the Submerged Membrane Bioreactor

The submerged membrane bioreactor (SMBR) is a promising technology for wastewater treatment and water reclamation. This paper presents results from two pilot scale SMBR systems operating in parallel on municipal wastewater in San Diego, Calif. The SMBRs were operated to address the limitations and advantages of the SMBR process compared to conventional activated sludge processes. Minimal membrane fouling was observed throughout the year of testing with the exception of the process limitations. Both pilot units provided consistently high quality effluents throughout the study, even when operating at hydraulic retention times as low as 1.5 h. Two sets of experiments were conducted to identify different fouling conditions. The first experiments were conducted to explore operation at high suspended solids concentrations. The SMBR process experienced adverse performance at mixed liquor suspended solids concentrations greater than approximately 20?g/L. The second experiments explored operation at low mean cell residence time (MCRT). At an MCRT of <2 days, membrane fouling was rapid. Chemical cleaning with sodium hypochlorite solution provided full recovery of the membrane permeability.     

Integration of Processes to Treat Wastewater and Source-Separated Urine

Human urine contributes 80% of the total nitrogen and 40–50% of the total phosphate load to municipal wastewater. This study examines the impact of separate urine collection and treatment on wastewater treatment. An integrated wastewater and urine treatment process was defined, in which single high-rate ammonium removal over nitrite and anaerobic ammonium oxidation processes and struvite recovery are at the heart of the nutrient management. The model study demonstrated that if 50% or more of urine were collected and treated separately, integrated wastewater treatment with more compact and energy-efficient processes would be possible. The integrated wastewater and urine treatment is compared to an existing state-of-the-art treatment process. The main advantage of urine separation is not only a better effluent quality. Existing processes including tertiary treatment can already produce very good effluent quality with total effluent nitrogen and phosphate concentrations of 2.5 and 0.5?g/m3, respectively. The main advantage of urine separation is the production of this same good effluent quality with a remarkable saving in resources. With sufficient urine separation, generation of net primary energy is possible.     

Evaluation of Mixing and Performance of Lab-Scale Upflow Anaerobic Sludge Blanket Reactors Treating Domestic Wastewater

The effects of varying hydraulic retention time (HRT) and associated upflow velocity on mixing and reactor performance were evaluated in five lab-scale upflow anaerobic sludge blanket (UASB) reactors treating real domestic wastewater. The mixing and transport studies were carried out with the help of tracer experiments at various HRTs using a pulse tracer input. A number of existing models were assessed for the analysis of the time series of observed tracer concentrations. The plug-flow reactor (PFR) model with two-zone dispersion better simulated the time series of tracer concentrations at all HRTs than other models, such as single compartment dispersion, completely mixed flow reactors (CMFRs) in series, and a combination of CMFR and PFR. The dispersion coefficients obtained from the two-zone dispersion model correlated well with the dispersion analysis expression for flow in a circular cylinder, and the correlation can be used for the prediction of dispersion in a UASB reactor. The analysis of reactor performance data indicated that reduction of dispersion owing to decrease in the upflow velocity resulted in increased sulfidogenic activity in the reactor. This was attributed to the inability of the sulfate reducers to colonize in the reactor at high upflow velocity and mixing condition.     

Wastewater Treatment with Biomass Attached to Porous Geotextile Baffles

A bench-scale study used nonwoven geotextiles as a compact biomass host media to treat wastewater from a combined sewer system. The geotextile coupons were used as baffles and suspended in an aerated reactor. Each baffle was offset in succession to form a sinuous channel with permeable boundaries. Filtering the total suspended solids (TSS) and micro-organisms formed a biomass floc in the interior of the baffles, which grew to emerge on the surface. Suspended and nonsettleable colloidal solids in the influent wastewater were captured by both filtration and adsorption from the channel flow. This bench-scale setup, named the geotextile baffle contact system, consistently provided secondary treatment to influent concentrations up to 318 mg/l of TSS and 114 mg/l of biological oxygen demand. Ammonia (NH3–N) concentrations were reduced over 90%, and mineralization of the nitrate (NO3–N) was also observed when the biofilm aged and thickened. Some of the influent TSS and sloughed biomass from the baffles settled to the bottom of the tank.     

Excess Sludge Production in Membrane Bioreactors: A Theoretical Investigation

This paper presents a theoretical investigation on excess sludge production in membrane bioreactors for municipal wastewater treatment. Based on mass balances of sludge and substrate, a formula to predict the excess sludge production in membrane bioreactors is introduced and verified by experimental data. The effects of kinetic parameters and operating conditions on excess sludge production are discussed for strong-, medium-, and low-strength municipal wastewaters, respectively. The strategy for reducing excess sludge production is recommended in order of priority, as sludge retention time→kd→Y→hydraulic retention time. Furthermore, the differences between membrane bioreactors and activated sludge processes are analyzed from the viewpoint of excess sludge production.     

Treatment of Dilute Wastewaters Using a Novel Submerged Anaerobic Membrane Bioreactor

Three 3?L laboratory scale submerged anaerobic membrane bioreactors (SAMBRs) with in situ membrane cleaning due to the bubbling of recycled biogas underneath them were studied for their ability to treat dilute wastewaters. Both Mitsubishi Rayon hollow-fiber and Kubota flat sheet membranes made of polyethylene with a pore size of 0.4?μm were used in this study, and the effect of different substrates (460?mg/L of glucose or synthetic) on chemical oxygen demand (COD) performance in the SAMBR was investigated. It was found that both membranes resulted in similar COD removals (>90% soluble COD at a hydraulic retention time of 3?h), but that the transmembrane pressure across the hollow fiber membranes was higher under similar conditions. Molecular weight analysis of the feed, reactor contents, effluent, and extracellular polymers using high pressure liquid chromatography showed that the membrane filtered out most of the high MW soluble organics, resulting in high COD removals. The experimental results from the SAMBR show the potential benefits of using this novel reactor design in a biological wastewater treatment process to minimize energy use and sludge production.     

Anaerobic Treatment of High Sulfate Wastewater with Oxygenation to Control Sulfide Toxicity

In this study, oxidation-reduction potential (ORP) was employed to regulate oxygen dosing for online sulfide toxicity control during anaerobic treatment of high sulfate wastewater. The experiment was conducted in an upflow anaerobic filter, which was operated at a constant influent total organic carbon of 6,740 mg/L [equivalent to a chemical oxygen demand (COD) of 18,000 mg/L], but with different influent sulfates of 1,000, 3,000, and 6,000 mg/L. The reactor was initially run at natural ORP (the system’s ORP without oxygenation) of about ?290 to ?300?mV and then was followed by oxygenation to raise ORP by +25?mV above the natural level for each influent sulfate level. At 6,000 mg/L sulfate under the natural ORP, methanogenesis was severely inhibited due to sulfide toxicity, and the anaerobic process was almost totally upset. Upon oxygenation by raising ORP to ?265?mV, the dissolved sulfide was quickly reduced to 12.2 mg S/L with a concomitant improvement in methane yield by 45.9%. If oxygen was not totally used up by sulfide oxidation, the excess oxygen was consumed by facultative bacteria which had been found to stabilize about 13.5% of the influent COD. Both sulfide oxidation and facultative activity acted as a shield to protect the anaerobes from an excessive oxygen exposure. This study showed that direct oxygenation of the recirculated biogas was effective to oxidize sulfide, and the use of ORP to regulate the oxygen dosing was practical and reliable during anaerobic treatment of high sulfate wastewater.     

2,4,6 Tri-Chlorophenol Containing Wastewater Treatment Using a Hybrid-Loop Bioreactor System

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and 30?days, while the feed COD (2600±100?mg?L?1), TCP (370±10?mg?L?1), and the hydraulic residence time (25?h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20?days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCP, COD, and toxicity removals. More than 95% of COD, TCP, and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120?mg?TCP?gX?1?day?1) at a sludge age of 20?days. TCP inhibition was eliminated by operation of the system at sludge age above 20?days to obtain nearly complete COD, TCP, and toxicity removal.