S. Yan

Extracellular polymeric substances (EPS) producing bacterial strains of municipal wastewater sludge: Isolation, molecular identification, EPS characterization and performance for sludge settling and dewatering

Wastewater treatment plants often face the problems of sludge settling mainly due to sludge bulking. Generally, synthetic organic polymer and/or inorganic coagulants (ferric chloride, alum and quick lime) are used for sludge settling. These chemicals are very expensive and further pollute the environment. Whereas, the bioflocculants are environment friendly and may be used to flocculate the sludge. Extracellular polymeric substances (EPS) produced by sludge microorganisms play a definite role in sludge flocculation. In this study, 25 EPS producing strains were isolated from municipal wastewater treatment plant. Microorganisms were selected based on EPS production properties on solid agar medium. Three types of EPS (slime, capsular and bacterial broth mixture of both slime and capsular) were harvested and their characteristics were studied. EPS concentration (dry weight), viscosity and their charge (using a Zetaphoremeter) were also measured. Bioflocculability of obtained EPS was evaluated by measuring the kaolin clay flocculation activity. Six bacterial strains (BS2, BS8, BS9, BS11, BS15 and BS25) were selected based on the kaolin clay flocculation. The slime EPS was better for bioflocculation than capsular EPS and bacterial broth. Therefore, extracted slime EPS (partially purified) from six bacterial strains was studied in terms of sludge settling [sludge volume index (SVI)] and dewatering [capillary suction time (CST)]. Biopolymers produced by individual strains substantially improved dewaterability. The extracted slime EPS from six different strains were partially characterized.

Potential use of filamentous fungi for wastewater sludge treatment.

Specific filamentous fungi (FF) have been recognized for sludge treatment and possibly these strains can be utilized for simultaneous bioflocculation, solids and pathogens reduction and, removal and degradation of toxic compounds. Based on current research work and findings, this review provides the state-of-art knowledge on the role of FF (or moulds) in sludge treatment. The proposed theories are presented, critically analyzed and future scope for specific research on utilization of FF for treatment of sludge is recommended.

Bacterial polymer production using pre-treated sludge as raw material and its flocculation and dewatering potential

Sterilization, alkaline-thermal and acid-thermal treatments were applied to different sludge solids concentrations (17.0; 22.4; 29.8; 37.3; 44.8 g/L, respectively) and the pre-treated sludge was used as raw material for Serratia sp.1 to produce extracellular polymeric substances (EPS). After 72 h of fermentation, total EPS of 2.3 and 3.4 g/L were produced in sterilized and alkaline-thermal treated sludge as compared to that of 1.5 g/L in acid-thermal treated sludge. Lower EPS were produced at relatively higher solids concentrations (37.3; 44.8 g/L). Broth, crude forms of capsular and slime EPS were extracted from fermented broths and used as conditioning agents by combining with 150 mg of Ca(2+)/L of kaolin suspensions. Maximum flocculation activity of 79.1% and increased dewatering by 52.2% was achieved using broth and crude capsular EPS, respectively. The results demonstrated that EPS having high flocculating capability could be produced using wastewater sludge as sole raw material.

Biochemical diversity of the bacterial strains and their biopolymer producing capabilities in wastewater sludge

The biochemical characterization of 13 extracellular polymeric substances (EPS) producing bacterial strains were carried out by BIOLOG. The bacterial strains were cultured in sterilized sludge for EPS production. Flocculation and dewatering capabilities of produced EPS (broth, crude slime and capsular) were examined using kaolin suspension combined with calcium (150 mg of Ca(2+)/L of kaolin suspension). BIOLOG revealed that there were 9 Bacillus, 2 Serratia and 2 Yersinia species. Most of these bacterial strains had the capability to utilize wide spectrum of carbon and nitrogen sources. EPS concentration of more than 1g/L was produced by most of the bacterial strains. Concentration of EPS produced by different Bacillus strains was higher than that of Serratia and Yersinia. Broth EPS revealed flocculation activity more than 75% for Bacillus sp.7, Bacillus sp.4 and Bacillus sp.6, respectively. Flocculation activity higher than 75% was attained using very low concentrations of broth EPS (1.12-2.70 mg EPS/g SS).

Polymer production by bacterial strains isolated from activated sludge treating municipal wastewater.

Polyhydroxyalkanoates (PHAs) accumulating bacteria were isolated from activated sludge samples collected from municipal wastewater treatment plants in Quebec. Twelve bacterial strains were screened for PHA production with acetate as sole carbon source. PHA granules exhibited a strong orange fluorescence when stained with Nile blue A observed under microscope (X100x). PHA was also analyzed by Gas Chromatography Linked to Mass Spectroscopy (GCMS) to further confirm the presence and the concentration of PHA. To compare the abilities of these PHA accumulating bacterial strains, synthetic media with acetate as carbon source was prepared to accumulate PHA in 500 mL Erlenmeyer flask containing 150 of the medium. These flasks were then inoculated with the isolated bacterial strains, incubated at 25 degrees C for 48 hours in a rotary shaker at 220 rpm. The results showed that the bacterial strains isolated from sludge possess different abilities for accumulating PHA. The maximum PHA content of 27.50% was obtained by strain PHA-SB3. The PHB/PHV ratio of the copolymer produced in the study changed in accordance with operating time and strains.

Methodology for the quantification of greenhouse gas emissions during land application of sewage sludge

Land application of sewage sludge improves soil physical, chemical and biological properties, minimizes the mineral fertilizer application and reduces maintenance of soil. In this work, various methods to estimate greenhouse gas (GHG) emissions due to land application of sewage sludge described in the literature were summarized and their limitations were presented. Moreover, an improved methodology to evaluate GHG emissions due to the land application of sewage sludge was proposed. Further, based on the proposed methodology, GHG emissions due to land application of sewage sludge at lower, higher and average concentrations of nutrients (carbon, nitrogen and phosphorus) were assessed. The results revealed that GHG emissions substantially decreased when higher nutrients containing sewage sludge were applied to land. For methodologies presented in the literature, GHG emissions or reductions due to land application did not change with nutrients concentrations of sewage sludge. However, based on the proposed methodology GHG emissions or reductions varied according to sludge nutrients concentrations.