| Bearing the properties of high viscosity, high moisture content and containingpathogenic bacterium and heavy metals, the sewage sludge is difficult to treat andutilize. Aerobic composting is a pratical way to make sludge into resourse, which is thegeneral trend to treat sludge nowadays. In this study, we discussed the feasibility ofco-composting of sludge and green wastes. In addition, we studied the contralparameters and the detecting parameters of windrow and in-vessel composting systemsduring the composting prosess. In this study, we had a brief research on sludgebiodrying technology and compared it with sludge compost technology, in order toprovide a reference when choosing the project of treating sludge and green wastes.The green wastes cut into slices have the properties of low moisture content, highC/N ratio and strong anti-pressure ability, and the test had showed that no matter whichtechnology we chose, including windrow composting, in-vessel composting andbiodrying, sludge and green wastes could be treated well.The best ratio of sludge and green wastes was3:1for the windrow composting.Under this condition, the maximum temperature of the windrow achieved71OC and itcould stay21d at above55OC. After44d, the moisture content of the windrow reduced to48%, and the contents of nutrient elements and heavy metals and the GI (germinationindex) of the windrow complied with the relevant provisions.When the green wastes were all recycled, and the ratio of sludge and green wasteswere2:1, as well as the ventilated intensity being90L/(h kgVS), there were best resultsfor the in-vessel composting. Under the conditions, the maximum temperature of thevessel-inside achieved66OC and it could stay4d during the high phase, complying withthe relevant provisions. After the primary fermentation of12d, the moisture content ofsludge reduced to48%and the VS reduced13%. The contents of nutrient elements andheavy metals could achieved the relevant provisions, however, the GI was only26%. Asa result, the compost was necessary to have a secondary fermentation.The influence of ventilated intensity on biodrying had been researched. The resultsshowed that the most suitable ventilated intensity is120L/(h kgVS), under whichcondition, the maximum temperature of the reactor-inside was66OC and it could stay 40h during the high phase. After111h, the moisture content of sludge reduced to55%,and the organic content of the treated sludge was high, which was beneficial to thefollow-up treatment.We can draw a conclusion that all the three technologies mentioned abovecan treat sludge and green wastes well, and the pH stayed between6.5to8.5during composting and biodrying processes, so there was no necessary to handgovern the pH. Windrow composting just needs small investment, and thecomposts are stable, however, it covers an area of great inconvenience andneeds a long time to make the compost stable. Besides, the exhaust gas producedduring the composting process is difficult to collect and treat. In-vesselcomposting need not a large area to operate, and the exhaust gas is easy tocollect and treat, as well as having a short cycle. But it needs a large investment,and the compost out from the vessel should have a secondary fermentation.Biodrying has a short process cycle and good collection of exhaust gas, with thepurposes of sludge conditioning, deodorizing and reducing the moisture content.Whereas, biodrying need a large investment as well. |
