Abstract
pH has an important effect on the physiological activity of eosinophilic microorganisms. Therefore, this study used excess sludge produced by the mixed treatment of leachate and municipal sewage to explore the impact of different sludge initial pH on microbial biochemical reactions associated with the performance of excess sludge dehydration. Shake-flask tests were performed using inoculated microorganisms and fresh excess sludge in 500 mL Erlenmeyer flasks at a ratio of 1:4, with the addition of 2 g/L S0 and 6 g/L FeS2 as energy sources. Erlenmeyer flasks were shaken for 72 h at 180 rpm and 28 °C, in a reciprocating constant homeothermic oscillating water-bath. Results show that the specific resistance to filtration (SRF) of the bioleached excess sludge decreased from (1.45~6.68) × 1012 m/kg to (1.21~14.30) × 1011 m/kg and the sedimentation rate increased from 69.00~73.00% to 81.70~85.50%. The SRF decreased from 1.45 × 1012 m/kg to 1.21 × 1011 m/kg and the sedimentation rate increased from 69.00% to 85.00%, which both reached the highest level when the initial pH of the excess sludge was 5 and the bioleaching duration was 48 h. At this time, the rates of pH reduction and oxidative redox potential (ORP) reached the highest values (69.67% and 515 mV, respectively). Illumina HiSeq PE250 sequencing results show that the dominate microbial community members were Thiomonas (relative abundance 4.59~5.44%), which oxidize sulfur and ferrous iron, and Halothiobacillus (2.56~3.41%), which oxidizes sulfur. Thus, the acidic environment can promote microbial acidification and oxidation, which can help sludge dewatering. The presence of dominant sulfur oxidation bacteria is the essential reason for the deep dehydration of the bioleached sludge.
Highlights
With the acceleration of industrial production processes and the improvement of living standards, sewage sludge production is increasing rapidly in China
The Specific resistance to filtration (SRF) decreased from 1.45 × 1012 m/kg to 1.21 × 1011 m/kg and the sedimentation rate increased from 69.00% to 85.00%, which both reached the highest level when the initial pH of the excess sludge was 5 and the bioleaching duration was 48 h
This study, focused on the increased difficulty of sludge dewatering after mixed treatment of leachate and municipal sewage, as well as the possible negative impact of the sludge initial pH
Summary
With the acceleration of industrial production processes and the improvement of living standards, sewage sludge production is increasing rapidly in China. Because sludge has a high water content and large volume, dehydration must be carried out to reduce sludge volume to facilitate transportation and subsequent treatment and disposal. Sludge, which is a hydrophilic colloidal particle with a high bound water content, is very difficult to dehydrate [2]; to achieve deep dewatering, preconditioning must be carried out. Commonly used methods include freezing and thawing [3]; ultrasound [4]; thermal hydrolysis [5]; and chemical coagulation [6]. These methods have certain treatment effects, there are still varying degrees of limitations. Freezing and thawing is most suitable for cold climates [7]; and Coatings 2020, 10, 989; doi:10.3390/coatings10100989 www.mdpi.com/journal/coatings
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
