Upgrading of Anaerobic Digestion of Waste Activated Sludge by Thermal Pretreatment

Abstract

The effect of thermal pretreatment on the characteristics of degradation of waste activated slduge (WAS) in anaerobic digestion was investigated by laboratory-scale batch and continuous experiments at 35±1°C. The pretreatment temperatures of WAS ranged from 62 to 175°C and the pretreatment times were 15, 30, 60, 90 and 120 minutes. The organic particulates in WAS were solubilized to soluble carbohydrates, lipids and proteins or converted into the lower molecular weight compounds, such as volatile fatty acids, by the thermal pretreatment. Through the thermal pretreatment. the anaerobic degradability of WAS and the gas production from WAS were greatly increased, and the retention time necessary for anaerobic digestion was possible to be reduced by 5 days. The optimum pretreatment temperature and pretreatment time for the upgrading of anaerobic digestion of WAS were 170°C and 60 minutes, respectively. At this pretreatment condition, the COD removal and the gas production were markedly increased. At the digester with retention time from 5 to 10 days, the COD removal efficiency reached over 60% and gas production ranged from 223 to 235ml·gCOD−1 which were about 2 times those of the control. The numbers of methanogenic bacteria existing at retention times from 1.5 to 10.0 days ranged from 107 to 108 MPN·ml−1, and reached the maximum population level at the retention time of 5 days. The increase in solubilization and anaerobic degradation of major organic compounds in WAS by thermal pretreatment decreased in the following order: carbohydrates > proteins > lipids.

A case study for a cost-benefit-based, stepwise optimization of thermo-chemical WAS pre-treatment for anaerobic digestion

“…The reduced disintegration efficiency at 100-120°C is in accordance with Li and Noike [25], who measured the solubilisation ratio of VS after thermal WAS PT from 30 to 170°C. Similarly, Kuglarz et al [26], who measured dissolved COD after thermal PT from 20 to 100°C, found stable but not increasing COD solubilisation rates as well as decreased ammonia and phosphate release from 70 to 100°C.…”

Biogas Production of Ozone and/or Microwave-Pretreated Canned Maize Production Sludge

“…The microwave irradiation at pH 2 resulted in significantly higher methane production comparing to ozonation, which could be explained by bigger efficiency in solubilization of chemicals and by the thermal effect of sludge treatment (Bougrier et al, 2006). The combined acidic and microwave treatment could significant accelerate the hydrolysis of organic matter, which is the limiting step of the microbial degradation (Li and Noike, 1992) (Table 1).…”

Microwaving human faecal sludge as a viable sanitation technology option for treatment and value recovery – A critical review

“…Thermal effects result from direct coupling of electromagnetic energy with water molecules, which raise the temperature of sludgy materials, decrease their viscosity and enhance their filterability. In addition, microwaves can selectively energize chemically bound water in sludge to facilitate its chemical dissociation and release of bound water (Li and Noike, 1992). In effect, the molecular heating effect of microwave irradiation facilitates the rapid disruption and disintegration of sludge flocs and bound water, and is responsible for improving dewaterability within a shorter (less than 2mins in most cases) heating time (Wojciechowska, 2005;Yu et al, 2009).…”