Pre-treatments to enhance the biodegradability of waste activated sludge: Elucidating the rate limiting step

• Published in: Biotechnology advances 2018-09, Vol.36 (5), p.1434-1469
• Main Authors: Gonzalez, A., Hendriks, A.T.W.M., van Lier, J.B., de Kreuk, M.
• Format: Article
• Language: English
• Subjects: Activated sludge; Anaerobic digestion; Anaerobic treatment; Anaerobiosis - physiology; Biodegradability; Biodegradation; Biodegradation, Environmental; Biotechnology; Carbohydrates; Heat treatment; Hydrology; Hydrolysis; Limiting factors; Methane - metabolism; Methane production; pre-treatment; Pretreatment; Proteins; Review; Sewage; Sewage sludge; Sludge; Waste Disposal, Fluid - methods; Waste-activated sludge; Water treatment
• ISSN: 0734-9750; 1873-1899
• DOI: 10.1016/j.biotechadv.2018.06.001

Pre-treatments for waste activated sludge (WAS) are, in most cases, an attempt to increase the biodegradation and/or improve hydrolysis rate of WAS after anaerobic digestion. This review presents an extensive analysis of WAS pre-treatments effectiveness focusing on increasing the biodegradability. In the first part of the review, WAS is considered as a cluster of organic components: proteins, carbohydrates, humic substances and cells. Based on this breakdown into components, the effect of different pre-treatments on each component (and in combination) is described. Also, possible reasons for the contradictory results frequently found among different studies dealing with the same pre-treatment are included. In the second part, the review describes the effects on volatile solids removal by digestion after pre-treatment and on the dewaterability of the final digestate. The energy balance and potential limiting factors for each pre-treatment are also taken into account. From the published works it is concluded that some pre-treatment techniques, such as thermal hydrolysis, thermal phased anaerobic digestion and low-temperature pre-treatment are effective ways to increase energy production and to improve other sludge properties, such as dewatering. However, these techniques are very energy intensive and require a large capital outlay, so research on milder pre-treatment techniques is valuable.