This research focuses on an evaluation of the performance of a new process being called the “anaerobic sequencing batch reactor” (ASBR). The ASBR operates on an intermittent, fill and draw regimen. This results in alternating high substrate/low substrate (feast/famine) conditions. The high substrate conditions right after feeding results in high rates of substrate conversion to biogas. The low substrate concentration near the end of the react sequence results in efficient bioflocculation and solids separation.

The temperature-phased anaerobic process involves a two-stage reactor system with the first stage operated at a thermophilic temperature (typically 55°C) and the second stage operated at a mesophilic temperature (typically 35°C). The purpose of this laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage mesophilic system for treating domestic wastewater sludge. Of particular interest in the research was a comparison of the two systems from the standpoint of coliform reduction, volatile solids destruction, and biogas production.The temperature-phased system achieved almost complete destruction of total and fecal coliforms over a range of solids retention times (SRTs) from 10 to 15 days. The concentration of fecal coliforms in the effluent from the temperature-phased system never exceeded I 000 MPN/g total solids, which can meet the U.S. federal fecal coliform requirements for Class A biosolids. At SRTs ranging from 10 to 15 days, the temperaturephased system achieved an 18% higher destruction of volatile solids and 16% more methane production than was possible with the singlestage mesophilic process.The regulations Standard for the Disposal of Sewage Sludge outline stringent pathogen requirements for wastewater treatment plants (WWTPs) that desire to sell or give away biosolids for application to land. One of the requirements for the land application of Class A biosolids is that fecal coliforms be less than I 000 most probable number per gram of total solids (MPN/g TS). Most WWTPs using conventional anaerobic digesters operated at a temperature of approximately 35°C with hydraulic retention times (HRTs) ranging from 12 to 30 days are not capable of meeting fecal coliform requirements for Class A biosolids.Thermophilic anaerobic digestion is an alternative approach that has advantages over mesophilic digestion in terms of pathogen destruction. A single-stage thermophilic anaerobic system (Garber, 1977) and a thermophilic two-phase system (Lee et al.. 1989) were used and both systems achieved a higher reduction in pathogens than a mesophilic anaerobic digester. But these processes could not avoid the disadvantages of thermophilic anaerobic digestion. Vo]atile fatty acids (VFAs) are high in the effluent (Fisher and Greene, ] 945, and Rudolfs and Heuke]ekian, 1.930) and odors from high VF As are more pronounced than for mesophilic systems. Also, when using thermophilic digestion, shock loadings or temperature changes can lead to unstable conditions and failure (Garber, 1977, and Garber et al., ]975). September/October 1997In laboratory studies using a synthetic substrate (nonfat dry milk), the temperature-phased anaerobic system was found to achieve significantly higher organic removals than are possible using single-stage systems operated at either 55 or 35°C (Harris and Dague, 1993; Kaiser and Dague, 1994 and ]995;Steinbach, 1994; and WeI per, 1995). Also, with the temperature-phased system, it is possible to operate at higher loadings than are possible wi...

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Pure cellulose with average diameters of 20 and 50 m were treated in laboratory-scale CSTRs to study the effect of pH, reactor hydraulic retention time (HRT), and substrate concentration on the rate of anaerobic acidogenesis for those two cellulose particle sizes. The pH effect was studied using a particle size of 20 rm at an HRT of 48 hours while controlling the pH at levels of 5.2, 5.6, 6.0, 6.4, and 6.8. After determining that a pH of 5.6 was optimum, the effect of HRT was evaluated by operating the reactors at HRTs of 24, 36, 48, 60, and 72 hours for both the 20 and 50 ^m cellulose sizes. After finding that an HRT of 48 hours was sufficient for acidogenesis, the effect of organic loading rate (OLR) was studied by varying the OLR between 2 and 8 g/L/day. The results of the research indicate that the conversion of particulate cellulose to soluble chemical oxygen demand (SCOD) ranged from 31% (pH 6.8) to 44% (pH 5.6). The HRT studies illustrated that a substrate with a smaller particle size (20 jum) and operation at a longer HRT resulted in a higher conversion to SCOD compared with a larger particle size (50 m) and operation at a shorter HRT. It was also observed that the effluent SCOD increased proportionally with increases in the influent particulate COD. Water Environ. Res., 66, 670 (1994).

The temperature-phased anaerobic bioreactor (TPAB) has been under study by Dague and co-workers at Iowa State University. The temperature-phased approach involves a two-stage reactor system with the first stage operated at a thermophilic temperature (commonly 55°C) and the second stage operated at a mesophilic temperature (commonly 35°C). The purpose of laboratory study was to compare the performance of the temperature-phased system with the conventional single-stage mesophilic system for treating mixtures of primary and waste activated sludge. Of particular interest in the research was a comparison of the two systems from the standpoint of coliform reduction, volatile solids (VS) destruction, and biogas production. The temperature-phased system achieved complete destruction of total and fecal coliforms over a range of SRTs from 11 to 28 days. The concentration of fecal coliforms in the effluent from the temperature-phased system never exceeded 1000 MPN/g total solids (TS), which can meet the U.S. Code of Federal Regulations, Title 40 (40 CFR), Part 503 coliform requirements for Class A sludge. At the optimal SRTs ranging from 11 to 17 days, the capacity of VS removal of temperature-phased system was more than double that of the conventional single-stage system. The foaming problem associated with the digestion of waste activated sludge was eliminated.