Prospects and problems of sludge pre-treatment processes

Abstract

Pre-treatment processes have been developed in order to improve subsequent sludge treatment and disposal. Disintegration of sludge solids in the aqueous phase changes the sludge structure and solubilizes organic matter. This paper provides an overview of the applications of wet disintegration in wastewater and sludge treatment. Applied disintegration techniques such as mechanical, thermal, chemical and biological methods are briefly described. The methods are compared regarding energy consumption, operational reliability and stage of development for application on wastewater treatment plants. Mechanical and thermal methods appear to be most suitable at this stage. The effects of pre-treatment on subsequent sludge treatment processes and the wastewater treatment are described. The performance of various methods is assessed. For the improvement of stabilization, mechanical and ozone treatment as well as thermal treatment perform best. Dewatering can be enhanced by thermal and freeze/thaw treatment. All methods show positive effects in the reduction of the number of pathogens. Pre-treatment leads to secondary effects like the generation of recalcitrant compounds and odor, which is mainly a problem of thermal and ozone treatment. The evaluation of capital and operational costs is difficult, because of the lack of full-scale experience. Especially thermal, freeze/thaw and biological treatments can be realized at low costs if the conditions are appropriate. Nevertheless, the economic efficiency has to be investigated critically for each individual application.

Effects of various pretreatments on biohydrogen production from sewage sludge

“…The experimental results suggested that the influences of the four pretreatments on the methanogens were different. This was reasonable since the function mechanisms of the four pretreatments on bacteria are different: acid pretreatment are depended on the free H + , alkaline pretreatment depended on the free OH − , thermal pretreatment depended on the high temperature and ultrasonic pretreatment depended on the temperature and the shear produced in the sonication [1,9] . Although there was no methane production in anaerobic fermentation of some sludge samples, the hydrogen consumption also occurred in the last stage of the fermentation because there were other hydrogen-consum- ing functions like homoacetogenesis, sulfate reduction, propionic acid production, and so on.…”

“…Some pretreatment methods, such as thermal pretreatment and alkaline pretreatment, have been used to disrupt the microbial cells and release the organics to liquid so as to enhance the anaerobic digestion of sludge [1,8,9] and biohydrogen production of sludge [10][11][12][13][14] . For example, Cai et al [10] utilized alkaline pretreatment to enhance hydrogen production from sewage sludge.…”

Effects of sludge pretreatment on sludge reduction in a lab-scale anaerobic/anoxic/oxic system treating domestic wastewater

“…SCOD released in the supernatant was found to be in the range 1,100-1,450 mg l -1 . Müller (2001) reported that the solubilization efficiency can be used as an index for the efficiency of sludge disintegration. In the present study, sludge solubilization efficiency (a) was calculated as the ratio of the soluble COD (SCOD) increase by thermochemical pretreatment to the total COD (TCOD) of the sludge before pretreatment as follows:…”

Biological hydrogen production from sterilized sewage sludge by anaerobic self-fermentation

“…The sludge was put into a 1 L conical flask (D × h = 10 cm × 20 cm) with stopper in the sterilization. Though the optimal temperature of thermal hydrolysis of sewage sludge was 170-175 • C [1,18], higher temperature would consume more energy. So, the conditions of thermal pretreatment were selected as 121 • C, 1.5 atm and 30 min of treatment time accordingly to the references [13,17,19].…”