Application of physico-chemical pretreatment methods to enhance the sludge disintegration and subsequent anaerobic digestion: an up to date review

Abstract

Anaerobic digestion of waste activated sludge (WAS) is most commonly used at wastewater treatment facilities to stabilize the sludge. However, poor biodegradation efficiency of sludge and longer retention times (20-30 days) are the major limitations of anaerobic digestion method, which can be overcome by disintegrate the sludge and make intracellular material readily available to anaerobic biodegradation. Several sludge disintegration techniques (Thermal, chemical and mechanical) and their combinations were studied previously in order to improve the anaerobic digestibility of sludge, reduce the sludge retention time and enhance the production of biogas. However, none of the pretreatment technique shows a real breakthrough in enhancement of anaerobic digestibility of WAS due to associated drawbacks, such as high operational and capital cost, poor sanitization and energy intensive. On the other hand, hybrid pretreatment techniques endow with promising outcomes through neutralizing the associated drawbacks with individual pretreatment techniques. Nevertheless, the research on the application of hybrid pretreatment techniques is in its infant stage, presently. Therefore, the satisfactory research in this direction can lead to policy maker and environmental protection agency to select more robust and sustainable solution for sludge treatment. This review encompasses the up-to-date information about the thermal, chemical and mechanical sludge disintegration techniques (principle, performance at lab, pilot and full scale, advantages and disadvantages). A comparative evaluation of these techniques are also presented in terms of COD solubilization, dewaterability, pathogens removal, lab/pilot/full scale application, capital and, operation and maintenance cost involved and energy requirement.

Optimization of H2O2 dosage in microwave-H2O2 process for sludge pretreatment with uniform design method

“…Obviously, sludge pretreatment becomes the key step for both sludge reduction based on the lysis-cryptic growth mechanism and enhancement of anaerobic sludge digestion. Therefore, recently many researchers have focused on sludge pretreatment technologies mainly based on physical, chemical, and biological methods and their combinations for minimization of sludge production, improvement of sludge dewaterability and enhancement of sludge anaerobic digestion (Neyens and Baeyens, 2003;Odegaard, 2004;Bordeleau and Droste, 2011;Chi et al, 2011;Coelho et al, 2011;Tyagi and Lo, 2011), and notably the hybrid sludge pretreatment technologies endow with promising outcomes through neutralizing the associated drawbacks with individual pretreatment techniques. As one of the most promising technologies, e.g., microwave pretreatment was proved to be the most effective for enhancing methane potential of pulp mill waste sludge, compared with ultrasonic and chemo-mechanical methods (Saha et al, 2011), studies of microwave technology and its combined processes for sludge pretreatment have received increasing attention in recent years.…”

Optimization and Performance of Moderate Combined Alkali and Microwave Pretreatment for Anaerobic Digestion of Waste-Activated Sludge

“…resistant to AD due to slow and incomplete hydrolysis, resulting in long retention time (20-50 days) and low degradation efficiency (20-50%) [5][6].…”

“…Some reviews have summarized and compared different kinds of mechanical, thermal, chemical, and biological treatment methods [3,5,7]. The low-impact pretreatment methods such as mechanical or biological generally increase speed of degradation, while high-impact methods such as thermal hydrolysis or oxidation are likely to improve both speed and degree of degradation [3].…”

“…Every single pretreatment method has its advantages and disadvantages. Hybrid techniques, which usually combine more than one physical and chemical method to achieve synergistic effects, are proven to further enhance the efficacy of AD by higher biogas production and solids reduction [5,8]. One of the promising hybrid methods is the combination of alkali and microwave pretreatment.…”

“…The combined alkali and microwave pretreatment has been proven to increase sludge solubilization and kill pathogens effectively [5,7]. But whether pretreatment can improve the dewatering performance of the sludge is questionable.…”