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A down-flow hanging sponge (DHS) reactor has been developed as a cost-effective wastewater treatment system that is adaptable to local conditions in low-income countries. A pilot-scale DHS reactor previously demonstrated stable reduction efficiencies for chemical oxygen demand (COD) and ammonium nitrogen over a year at ambient temperature, but the pathogen reduction efficiency of the DHS reactor has yet to be investigated. In the present study, the reduction efficiency of a pilot-scale DHS reactor fed with municipal wastewater was investigated for 10 types of human pathogenic viruses (norovirus GI, GII and GIV, aichivirus, astrovirus, enterovirus, hepatitis A and E viruses, rotavirus, and sapovirus). DHS influent and effluent were collected weekly or biweekly for 337 days, and concentrations of viral genomes were determined by microfluidic quantitative PCR. Aichivirus, norovirus GI and GII, enterovirus, and sapovirus were frequently detected in DHS influent, and the log10 reduction (LR) of these viruses ranged from 1.5 to 3.7. The LR values for aichivirus and norovirus GII were also calculated using a Bayesian estimation model, and the average LR (±standard deviation) values for aichivirus and norovirus GII were estimated to be 1.4 (±1.5) and 1.8 (±2.5), respectively. Quantitative microbial risk assessment was conducted to calculate a threshold reduction level for norovirus GII that would be required for the use of DHS effluent for agricultural irrigation, and it was found that LRs of 2.6 and 3.7 for norovirus GII in the DHS effluent were required in order to not exceed the tolerable burden of disease at 10-4 and 10-6 disability-adjusted life years loss per person per year, respectively, for 95% of the exposed population during wastewater reuse for irrigation.

A practical-scale down-flow hanging sponge (DHS) reactor using third-generation (G3) sponge carriers was applied for treatment of the effluent from an up-flow anaerobic sludge blanket (UASB) reactor treating municipal sewage. The process performance of the DHS reactor filled with G3 sponge carriers (DHS-G3) was evaluated by conducting an on-site experiment in India over one year. The performance of the DHS-G3 for removal of organic matter and ammonium-nitrogen at a relatively short hydraulic retention time (HRT) of only 0.66 h satisfied the Indian effluent quality standards except for fecal coliform. The removal rate constants for total biochemical oxygen demand (BOD) and fecal coliform determined based on the water quality profiles along the DHS-G3 almost reached equilibrium approximately four months after the start of operation, i.e., 2.45 h(-1) for BOD and 2.30 h(-1) for fecal coliform, respectively. The oxygen utilization activity of retained sludge was determined to assess the distribution of heterotrophic and autotrophic bacteria along the DHS-G3. Nitrification was promoted in the lower portion of the DHS-G3 reactor in the duration with low organic load, while it decreased when the organic load was increased, probably due to proliferation of heterotrophic bacteria.

A rapid quantification method, based on Fourier transform near-infrared (FT-NIR) spectroscopy, was developed and validated to nondestructively quantify the concentrations of volatile fatty acids and ethanol in the effluent of an anaerobic H(2)-producing bioreactor. The first-derivative spectra calculated by a simple numerical difference, combined with the orthogonal signal correction method, were used as spectral preprocessing options. A calibration model was established and validated using gas chromatography measurement results. The number of internal latent variables was optimized based on the lowest root-mean-square error of calibration. The calibration model established shows the satisfactory results for the lowest root-mean-square errors of prediction compared to other preprocess methods. The method developed in this work is demonstrated to be more flexible compared with other approaches to determine the concentrations of volatile fatty acids and ethanol in the anaerobic reactor effluents.

Despite of the significance of the anaerobic digestion of lignocellulosic materials, only a limited number of studies have been carried out to evaluate the lignocellulosic digestion kinetics, and information about the modeling of this process is limited. In this work, a mathematical model, based on the Anaerobic Digestion Model No.1 (ADM1), was developed to describe the anaerobic conversion of lignocellulose-rich aquatic plants, with cattail as an example, by rumen microbes. Cattail was fractionated into slowly hydrolysable fraction (SHF), readily hydrolysable fraction (RHF) and inert fraction in the model. The SHF was hydrolyzed by rumen microbes and resulted in the production of RHF. The SHF and RHF had different hydrolysis rates but both with surface-limiting kinetics. The rumen microbial population diversity, including the cattail-, butyrate-, acetate- and H(2)-degraders, was all incorporated in the model structure. Experiments were carried out to identify the parameters and to calibrate and validate this model. The simulation results match the experimental data, implying that the fractionation of cattail into two biodegradation parts, i.e., SHF and RHF, and modeling their hydrolysis rate with a surface-limiting kinetics were appropriate. The model was capable of simulating the anaerobic biodegradation of cattail by the rumen cultures.

Anaerobic acidogenesis of Canna indica L. (canna) by rumen cultures was investigated in this study. Fractional factorial design (FFD) was used to explore the roles of the growth factors such as substrate concentration and pH in such a bioconversion, whereas response surface methodology (RSM) was employed for optimizing this acidogenic process. The optimum substrate concentration and pH for the acidogenesis of canna were found to be 8.2 g VSl(-1) and 6.6, respectively, and the corresponding degradation efficiency of canna was 52.3%. Volatile fatty acid yield peaked at 0.362 g g(-1)VS degraded at a substrate concentration of 6.9 g VSl(-1)and pH 6.7. These results were confirmed by the experimental results.

This study compares the performance of a pilot-scale combination of UASB and DHS system to that of activated sludge process (ASP) for the treatment of municipal sewage. Both systems were operated in parallel with the same sewage as influent. The study was conducted for more than 300 days, which revealed that organic removal efficiency of UASB+DHS system was comparable to that of ASP. Unfiltered BOD removal by both systems was more than 90%. However, UASB+DHS system outperformed ASP for pathogen removal. In addition, volume of excess sludge production from UASB+DHS was 15 times smaller than that from ASP. Moreover, unlike ASP, there is no requirement of aeration for the operation of UASB+DHS system, which makes it an economical treatment system. Considering the above observations, it was concluded that UASB+DHS system can be a cost-effective and viable option for the treatment of municipal sewage over ASP, especially for low-income countries.

The mechanism of faecal coliform removal in down-flow hanging sponge (DHS) system treating up-flow anaerobic sludge blanket (UASB) reactor effluent was the subject of this study. The results obtained revealed that the most important removal mechanism of faecal coliform in the DHS system is adsorption, followed by predation. Die-off is a relatively minor removal mechanism in the DHS system. The impact of physical and chemical factors such as contact time, effective sponge bulk volume and pH values on faecal coliform removal has been investigated. Increasing the contact time and sponge bulk volume exerted positive effect on the removal of faecal coliform. Changing the pH values between 6.5 and 9.0 did not show significant impact. Reducing sponge pore size from 1.92 to 0.56 mm, increased faecal coliform removal by a value of 1.3 log10.

Micro-electrodes were applied to anaerobic granular sludge, which was developed in a UASB reactor, to examine intra-granule profiles with respect to pH, glucose and sulfide. When glucose was employed as a bulk liquid substrate, the micro-electrodes study demonstrated the pH behavior along granule depth: pH decrement at the granule exterior portion due to acid formation (buildup of acidity), and subsequent pH increment at the granule inner portion due to the consumption of acid (buildup of alkalinity). Sulfide micro-electrode proved sulfate reduction that mostly occurred at the granule exterior portion. Chemical equilibrium consideration evidently explained the occurrence of ferric sulfide predominantly in the interior portion, which accounts well for the morphology of a representative double-layered structure of granules grown on a low level of sulfite. Inorganic elements distribution within anaerobic granule was examined by electron probe X-ray micro analysis (EPMA) and ICP methods. The presence of crystalline calcium carbonate (calcite) was identified by X-ray diffraction analysis.

Two UASB reactors were in parallel operated over two years, the one receiving a sulfate-rich wastewater (2000 mg COD l −1 versus 1000 mg SO 4 2− -S l −1 ), and the other receiving a sulfate-poor wastewater (2000 mg COD l −1 versus 33 mg SO 4 2− -S l −1 ), in order to compare the process behaviors with each other. Vial activity tests revealed that undissociated hydrogen sulfide caused an inhibitory effect more seriously on methane producing bacteria, rather than on sulfate reducing bacteria. In order to alleviate sulfide inhibition, a sulfide-stripping device was incorporated in the sulfate-rich UASB reactor. As a result, the sulfate-rich UASB accommodated successfully a sulfate loading of 1.3 kg SO 4 2− -S m −3 d −1 with 90% COD removal. The COD elimination carried out in the sulfate-rich UASB was associated with no methanogenesis, but was thoroughly performed by sulfate reducing bacteria solely. Hydrogen-utilizing methanogens were completely excluded from the sulfate-rich sludge consortium by proliferation of hydrogen-utilizing sulfate reducers.

The mutual interaction between sulfate-reducing bacteria (SRB) and methane-producing bacteria (MPB) in anaerobic sludge consortia was investigated using three identical laboratory-scale UASB reactors. Reactors were fed in parallel with a synthetic low strength waste (starch and sucrose, 500 mg COD l−1), but with different levels of sulfate (30, 150, 600 mg SO42- l−1, respectively). The mass balances of COD and sulfur over the experimental period of 180 days operation indicated that the higher the level of sulfate the less methane production caused since a greater electron flow was distributed to the SRB. Namely, at the last stage of the experiment in which the highest sulfate level was imposed, 75% of the total COD removal was performed by SRB. The specific methanogenic activities (SMAs) of the respective sludges were evaluated using the serum vial test using different substrates and by setting different sulfate levels. SMA was not affected by the presence of sulfate in the vials when acetate was used as the vial substrate. In the case of glucose as the test substrate, SMA increased with an increase in sulfate level. On the other hand, SMA decreased with increasing sulfate level when hydrogen was employed as the test substrate. A large amount of propionate accumulation was observed during vial tests, in which glucose was fed to the sludge grown at higher levels of sulfate, when zero or low levels of sulfate were added to the vials. This result suggests that SRB played an important role in the breakdown of propionate either through direct utilization or through a so-called interspecies hydrogen transfer.

Combining the processes of partial nitrification and anaerobic ammonium oxidation (ANAMMOX) is an attractive wastewater-treatment technology for nitrogen removal. In this study we investigated partial nitrification by implementing a closed down-flow hanging sponge (DHS) reactor operated at controlled oxygen concentrations. Basic concept of DHS process is similar to that of trickling filter, in which oxygen concentration can be easily manipulated by controlling airflow to the reactor. The closed reactor was fed with artificial wastewater containing NH(4)Cl and operated with an HRT of 1.5h at 30 degrees C. Oxygen inside the reactor was maintained below 3% (1.2mgDO x L(-1)) (DO-dissolved oxygen) except during the startup periods. Five months of continuous operation showed that there was a strong relationship between oxygen concentration and nitrite production. The ratio of nitrite produced relative to ammonium oxidized increased by decreasing oxygen concentration. Partial nitrification was satisfactorily accomplished under oxygen limitation at around 0.5% in the gas phase (0.2mgDOL(-1)). The system showed a high ammonium-removal rate, at a maximum of 1.46kg NH(4)(+)-Nm(-3)day(-1), even at limited oxygen concentration. We also found that oxygen concentration played an important role in the production of nitrous oxide, which increased with decreasing oxygen concentration.