Study On Impacts Of Steam Explosion Pretreatment Technique On Anaerobic Digestion Of Sludge

The traditional sludge anaerobic digestion method has many disadvantages，such as Low hydrolysisreaction rate、low gas production and gas production rate、large pool body area，and so on.In this paper, apretreatment technology was used, which can destroy the sludge microbial cell structure, release organicmatter, improve hydrolysis rate of the sludge, so as to achieve to enhance biogas production rate ofsludge anaerobic digestion. In previous research, the team found that a new pretreatment technology,namely, steam explosion pretreatment, can improve the sludge anaerobic digestion performanceobviously. This study compared the effect of steam explosion pretreatment on the physicochemicalproperties of sludge treatment，and its effect on wet and dry fermentation. Finally, this paper analyze theimpacts of steam explosion pretreatment technology on the morphology and distribution of the heavymetals, and the main conclusions are as follows:(1) After steam explosion pretreatment, sludge floc structure was damaged, the extracellularpoly-mers (ECP) of microorgan in the sludge will be dissolved in the process of high pressure and hightemperature. Dissolving organic matter changed dramatically, its concentration increased with the risingof pressure, and biodegradability also improved significantly.(2) After30days of fermentation, the gas production of untreated sludge is only40ml, but thegas production of1MPa and1.5MPa under the steam explosion treatment increased obviously, up to320ml and460ml respectively, and there was a positive correlation between the increase of SCOD andthe gas production. Along with the increase of pressure, the conversion rate of COD, TS and VS ofsludge in the anaerobic digestion were increased. The TS, VS and COD removal rate were respectivelyincreased by31.37%,82.36%and43.46%in1.5MPa, compared with the untreated sludge, theremoval rate were respectively increased by125.15%,351.23%and299.50%.(3) In dry fermentation experiment, the accumulation gas production of untreated sludge is67ml.However, the experiment of2.0MPa-90s increased by213.43%, the accumulation of gas productionshow a steady growth trend. There are four curves:2.0MPa-120s，3MPa-90s,2.5MPa-90s,2.5MPa-120s,which are arranged from bottom to the top, and the difference of cumulative gasproduction is small, but the gas production increased by422.39%,447.76%,452.24%and447.76%respectively compared with untreated sludge, and the gas production rate increased by482.84%~976.87%. In this paper, we choose the pressure2.5MPa and the retention time of90s as thebest parameters of the steam explosion pretreatment for anaerobic fermentation. The experimentalprocess shows that the filamentous bacteria in sludge has an impact on the gas production, the higherthe pressure, the lower gas production.(4) The concentration of heavy metals in the supernatant fluid increased obviously after highpressure homogeneous pretreatment. The cadmium and nickel increased by80.70%and74.58%separately, and the copper and chromium increased by52.24%and54.70%respectively. Heavy metals in organic state are transformed into carbonate bounded form, which is the main reason for theincreasing of leaching concentration of heavy metal, but it has little influence on heavy metal speciationof cadmium.