Resource Utilization Of Surplus Activated Sludge Based On Sludge Disruption

The surplus activated sludge (SAS) from municipal wastewater treatment plant containsvolatile fatty acids, humic acids, protein and other organic substances, and is rich in nitrogen,phosphorus, potassium, calcium and magnesium. And thus the SAS has potential use value.Recycling valuable substances and energy from the SAS can treat and dispose the SAS, andcan also partly compensate the operational fee for the municipal wastewater treatment plant.In the current study, the releasing characteristics of organic substances and nutrient during theSAS disruption were well known by a comparison of the four pretreatment methods (alkalinehydrolysis, ClO2oxidation, ultrasound, and homogenization) for sludge disintegration. Basedon this, the disrupted SAS by homogenization was tested for carbon source; the alkalinehydrolysis SAS was tested for phosphorus recycle by struvite precipitation; a new processcomprised of alkaline hydrolysis and anaerobic digestion was used for fast methaneproduction from the SAS, and the integration of phosphorus reclaim and anaerobic digestionwas applied for comprehensive SAS usage. The main results were as follows:(1) Organic substances and nutrient releases were different for the four pretreatmentmethods for sludge disintegration. Organic substances release was analyzed, and morphologyof SAS was observed after the disintegration. It suggested a different action mechanism. Itwas thought that the disrupted SAS by different pretreatment methods had their ownappropriate usage.（2）An evaluation of disparity between theory value and actual value demonstrated thatthe homogenization selectively released carbon from the SAS, with a cost lower than alkalinehydrolysis, ClO2oxidation, and ultrasound. The nutrient removal was improved above20%after a usage of carbon source from the disrupted SAS by homogenization. Inert substance(ash, heavy metals and PAH) in the SBR was monitored. It indicated that the accumulation ofinert substance contained in the disrupted SAS was negligible. The accumulation pattern wasproved to meet the Patterm Ⅰ model by statistic analysis. The inert substances in the SBRmaintained a dynamic equilibrium. Therefore, the usage of homogenization disrupted SAS asa carbon source for SBR was feasible. （3）TP and Ortho-P releases for single stage alkaline hydrolysis were62.86%and35.43%respectively, but the supernatant was above12.4, which was beyond the pH demand forstruvite precipitation. And thus two stage alkaline hydrolysis system (TSAHS) was developed.It maintained the alkaline hydrolysis supernatant below10. The operational conditions of theTSAHS were optimized by response surface method, where TP and Ortho-P releases achieved56.60%and40.70%, with pH kept at10.35.71%of TP and46.88%of Ortho-P were recycledunder the conditions of Mg/P molar ratio of1.8and reaction time of15min.16.54%of NH3-Nwas also recycled. X-ray spectrometer and chemical composition analysis confirmed theexistence of struvite in the precipitation. Hence, the TSAHS was capable for phosphorusrelease, and the released phosphorus was easy for recycle.（4）Ahigh organic substances release (about20%) was obtained by the TSAHS, and thebiodegradability of its supernatant was super. The supernantant (with pH9.9) was directlyused for anaerobic digestion, without a pH adjustment. The methane production achieved392±2mL CH4/gCOD at inoculums ratio of60%, with HRT only12h. It was much shorter thanthe HRT20d for anaerobic digestion of sludge. The TSAHS adjusted pH condition based onalkali neutralization capacity of the SAS. The anaerobic digestion system avoided a volatilefatty acids accumulation and maintained a constant pH for the system, which benefited themethane production.（5）Both processes of two stage alkaline hydrolysis-struvite precipitation-anaerobicdigestion and two stage alkaline hydrolysis-anaerobic digestion-struvite precipitation wereestablished after an integration of recycle technologies. The operation of both processes wasstable. An economic assessment suggested that both processes were economically feasible,with a net earning above200000CNY per year. A rate limiting step for both processes wasthe two stage alkaline hydrolysis, which needs further optimization.