Research On Temperature Staged And Biologically Phased Anaerobic Digestion System Of Waste Activated Sludge

In recent years, with the rapid development of WWTPs and the increase of sewagetreatment rates, sewage treatment capacity has substantially increased, resulting in acorresponding increase in sludge production. Sewage sludge has become a prominentglobal environmental problem. Anaerobic digestion is an established technology that iseffective and economical for the stabilization of sewage sludge and renewable energy canbe generated in the process of the degradation of organic matter at the same time.Therefore, it is very potential for the treatment and disposal of sludge. However, anaerobicdigestion technology is not popular in China and most of the exsiting anaerobic digestivesystems didn’t run very well. The concept of temperature staged and biologically phased(TSBP) was proposed to enhance the performance of waste-activated sludge (WAS)anaerobic digestion in this paper and the separation of acidogenic and methanogenic phasewas achieved by simultaneously controlling temperature and hydraulic retention time(HRT). Furthermore, thermal-alkaline pretreatment and TSBP anaerobic digestion processwere combined to discuss the efficiency of high solid content WAS treatment.The effect of temperature and HRT for acidogenic phase was disccused through batchtests and semi-continuous experiments, respectively. The results showed that theinfluences of temperature on the hydrolysis and acidification processes were different. Thedegree of solubilization gradually increased with the increase of temperature while whilethe acidification degree was highest at45°C. Compared with HRT of2and6days,4dayswas chosen as the appropriate HRT at45°C.TSBP anaerobic digestion system combined the acidogenic reactor (45°C,4days)with the methanogenic reactor (35°C,16days) was estabilished based on the operatingconditions of acidogenic phase and compared gas production and volatile solid reductionwith a single-phase system. The results showed84.8%and11.4%higher methane yieldand volatile solid reduction, respectively. Moreover, different microbial morphologieswere observed in the acidogenic and methanogenic phase reactors, which resulted fromthe temperature control and HRT adjustment. Applied TSBP anaerobic digestion system to high solid content (about8%) WAStreatment and thermal-alkaline pretreatment technology was added before the system.Batch tests were carried out to optimize the thermal-alkaline pretreatment condition andthe results explained that the hydrolysis process could significantly be promoted whendosing KOH solution to adjuste the initial pH value of sludge to11.0and then heating thesludge at80oC for30min. Moreover, after hydrolysis and acidification reaction in batchtests, the concentration of soluble chemical oxygen demand（SCOD）and volatile fattyacids（VFAs）were significantly higher than non-pretreated sludge. And the methanogenicpotential of thermal-alkaline pretreated WAS after hydrolysis and acidification processwas significantly higher than non-pretreated sludge. Combining thermal-alkalinepretreatment technology and TSBP anaerobic digestion system, the methane yield andvolatile solid reduction were both improved compared with single-phase syetem as well asTSBP anaerobic digestion system.A full-scale TSBP anaerobic digestion project was established based on the results ofthe laboratory research. The discussion was focusd on energy balance calculation andanalysis of the entire system to evaluate the application potential in terms of economy.And the TSBP anaerobic digestion system was able to achieve stable operation and realizeenergy self-sufficiency from the point of view of energy balance.