Laboratory studies on the temperature‐phased anaerobic digestion of domestic primary sludge

Abstract

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...

Effect of Sludge Dissolved Organic Matter on Oxidation of Ferrous Iron and Sulfur by Acidithiobacillus Ferrooxidans and Acidithiobacillus Thiooxidans

“…DERIVED FROM SLUDGE SAMPLES Malina and Pohland (1992) and Han et al (1997) have noted that low molecular weight organic acids are common metabolites of anaerobic digestion of sewage sludge. For example, the concentration of acetic acid ranging from 26.67 to 36.67 mM was produced in the anaerobic digestion process of domestic primary sludge with 5.0% of total solids.…”

Swine Wastewater Treatment in Anaerobic Digesters With Floating Medium

“…However, such lagoons are vulnerable to severe weather conditions. In North Carolina, Hurricane Floyd broke several swine waste treatment lagoons in 1999, resulting in waste contamination in receiving watercourses.Anaerobic digestion has been widely used for the treatment of high-strength industrial wastewaters and municipal waste sludge (Colleran et al, 1998;Dinsdale et al, 1997;Fitzgerald, 1996;Hamdi, 1996;Han and Dague, 1997;Lu et al, 1995;Maloney et al, 1998;Ruiz et al, 1997). It has also been applied to swine waste treatment (Boopathy, 1998;Cseh et al, 1984;Hill and Bolte, 2000;Lo et al, 1994 Montalvo, 1995).…”

Anaerobic Digestion at 45°C for Sludge Treatment: A Trade-off between Performances and Capability in Producing Class a Biosolids

“…This technique was likely to lead to the development of a population that was different from a population obtained through a true thermophilic digester. The population was most probably a thermo-tolerant acetate-utilizing mesophilic methanogens, a mesophile that can survive at high temperature but whose optimum growth rate occurs at mesophilic temperatures [19]. Thus, the operating temperature of 45°C might not be the optimum temperature for the microbes, hence affecting their methanogenic activity.…”