Hydrolysis and acidification of waste-activated sludge in the presence of biosurfactant rhamnolipid: effect of pH

Abstract

In this investigation, the effect of pH (4.0-11.0) on waste-activated sludge (WAS) hydrolysis and acidification in the presence of a biosurfactant rhamnolipid (RL) were studied. The results showed that the hydrolysis and acidification of WAS in the presence of RL at alkaline pH values were more efficient than that at acidic and near-neutral pH values. After 6 h of hydrolysis, the soluble protein and carbohydrate were 1,654.7 and 675.9 mg/L (pH 11.0), and 825.6 and 376.0 mg/L (pH 7.0), whereas the values were only 315.0 and 84.0 mg/L at pH 4.0 and 164.1 and 32.0 mg/L for the blank, respectively. After 2 or 3 days of fermentation, the accumulated short-chain fatty acids (SCFAs) reached the highest and then decreased with a further increase in time at all investigated pH values. The analysis of SCFA compositions showed that acetic, propionic, and iso-valeric acids were the three main products at any pH value. A higher pH contributed to a greater proportion of acetic acid and a lesser proportion of iso-valeric acid; a lower pH resulted in a greater proportion of iso-valeric and lesser proportion of acetic acid in the initial fermentation. The proportions of acetic acid for the system with biosurfactant RL addition were 16.65, 36.33, and 62.94 %, respectively, at pH 4.0, 7.0, and 11.0 after 1 day. Correspondingly, the proportions were 40.34, 12.60, and 11.01 % for iso-valeric acid.

Accelerating the sludge disintegration potential of a novel bacterial strain Planococcus jake 01 by CaCl2 induced deflocculation

“…This may be due to biosurfactant activity of the inoculated bacteria which caused a large amount of colloidal and insoluble organic into soluble organics. Most of the bacteria found in WAS are mainly gram negative bacteria of which the external membrane is made up of lipopolysaccharides (LPS) and phospholipids covalently linked to peptidoglycan layer through hydrophobic interactions (Luo et al, 2013). Sotirova et al (2009) have reported that biosurfactant may bind to the outer membrane of the bacteria and releases the LPS thereby enhancing the solubilization efficiency.…”

“…4a. It was expected that the deflocculating agent CaCl 2 decreases the cohesiveness of the floc matrix and the subsequent biosurfactant producing bacteria improves the solubilization by utilizing the disintegrated organic matters of the flocs thereby increasing the cell permeability and accelerating the release of significant levels of extracellular proteins and carbohydrates (Luo et al, 2013). The release profile of these soluble compounds was divided into 2 stages i.e.…”

“…To accelerate the degradation and to enhance the production of biogas various pretreatment methods can be employed (Appels et al, 2008). The biodegradability of the sludge can be improved by a variety of pretreatment methods such as chemical addition, thermal treatment , mechanical or ultrasonic disintegration (Dewil et al, 2006) and oxidative (Appels et al, 2011;, chemo mechanical toxicity, better environmental compatibility, biodegradability and effectiveness (Luo et al, 2013). Commercially available biosurfactants are considered to be very costly.…”

Physicochemical properties of sewage sludge disintegrated with high pressure homogenization

“…The activated sludge processes produce a large amount of excess sludge, which may cause a serious of environmental and health issues. Cost of sludge treatment and disposal accounts for about half or even up to 60% of the total cost in wastewater treatment plants (WWTPs) (Luo et al, 2013). To minimize and utilize the excess sludge is becoming the most important and challenging problems in the field of wastewater treatment (Zhang et al, 2009).…”

Hydrolysis and volatile fatty acids accumulation of waste activated sludge enhanced by the combined use of nitrite and alkaline pH

“…However, the major issue of this technology is the huge amounts of generated waste activated sludge. In China alone, about 4.6 million tons of dry sludge was produced in 2012 (Ministry of Housing and Urban-rural Development of China 2013), and the cost of sludge treatment accounts for 20-60 % of capital and operation costs of WWTPs (Luo et al 2013). Therefore, the disposal of WAS became one of the most important issues for WWTPs.…”