Effect of C/N ratio on extracellular polymeric substances (EPS) and physicochemical properties of activated sludge flocs

Activated sludge process has been applied worldwide in municipal and industrial wastewater treatment practices. Excess sewage sludge, produced in sedimentation after wastewater bio-treatment, is an inevitable by-product of wastewater treatment processes. In any case sludge treatment and disposal should always be considered as an integral part of treatment of wastewater. Currently, the most widely available options in the world are the agriculture utilization, the waste disposal sites, the land reclamation and restoration, the incineration and other novel uses. Extracellular polymeric substances (EPS), as high-molecular weight compounds are secreted by activated sludge microorganisms, which can significantly influence the physicochemical properties and function of activated sludge flocs. Because of the crucial roles of EPS, many researchers have been made to explore their chemical compositions and physicochemical properties. Polysaccharides, humic substances and proteins are usually found to be the major components of EPS. The present paper sought to review past and future trends in sludge handling, focusing mainly at the organic matters.

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Improvements on activated sludge settling and flocculation using biomass-based fly ash as activator

Scientific Reports ◽

10.1038/s41598-019-50879-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 1

Author(s):

Xiaoqian Chen ◽

Fangong Kong ◽

Yingjuan Fu ◽

Chuanling Si ◽

Pedram Fatehi

Keyword(s):

Fly Ash ◽

Activated Sludge ◽

Extracellular Polymeric Substances ◽

Sem Analysis ◽

Sludge Flocs ◽

Before And After ◽

Number Of Microorganisms ◽

Adverse Influence ◽

Settling Performance ◽

Sludge Settling

Abstract Biomass-based fly ash and wastewater are undesired products of the pulping industry. Recently, the use of biomass-based fly ash as an adsorbent (i.e., a valued material) for constituents of wastewater effluents was reported. In this work, the settling performance and properties of activated sludge were studied in the presence of fly ash. Upon mixing, fly ash increased the zeta potential of the sludge from −31 mV to −28 mV, which was due to the release of cationic ions from fly ash in the sludge suspension. The sludge settling and its flocculation affinity were improved through the complexation of flocs and released cation ions from fly ash. The relationships between the protein/polysaccharide (PN/PS) ratio and the content of extracellular polymeric substances (EPS) as well as the ratio and the properties of the sludge flocs were determined. A correlation between the total loosely bound-EPS (LB-EPS) content and the effluent suspended solids (ESS) (Pearson’s coefficient, rp = 0.83) was observed. The performance of sludge flocculation and settling were much more closely correlated with LB-EPS than with tightly bound EPS (TB-EPS). Scanning electron microscopy (SEM) analysis of sludge flocs before and after EPS extraction showed that the sludge flocs contained a large number of microorganisms, mainly Bacillus and Cocci. The amount of LB-EPS had an adverse influence on bioflocculation, effluent clarification and sludge settling affinity. The sludge properties had a moderate relationship with the PN/PS ratio of LB-EPS. Also, no correlation could be established between the ratio and the TB-EPS content.

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