Preparation Of Sludge Hydrolyzate-Trichoderma Fermentation Compound Foliar Fertilizer And Its Promoting Effect On Cucumber And Chinese Cabbage

The activated sludge process is the most commonly applied biological wastewater treatment technology,but this process produces a tremendous amount of unused biomass,which has to be removed from the treatment system as excess sludge.The excess sludge contains plenty recoverable organic matter and nutrients though it also contains harmful substances such as heavy metals,pathogenic microbes and malodorous gas,etc..Previous researches have showed that thermal alkaline hydrolysis technology in a closed container with temperature>150℃ and alkali as catalysts can inactivate all pathogenic microbes,hydrolyze biomass,and precipitate and deactivate heavy metals.We assumed that thermal alkaline hydrolysis technology may be one of the effective ways in detoxifying and recycling excess sludge.The objectives of the present paper are to study the process of thermal alkaline hydrolysis of excess sludge and the charactritics of its hydrolysates,to explore the effect of addition of the hydrolysates on solid state fermentation of Trichoderma with rice straw,to study the possibility of using the mixture of hydrolysates and Trichoderma ferment as foliar fertilizers,and to study the effect of the prepared foliar fertilizers on the growth of cucumber and Chinese cabbage.Main results are as follows.1.The results from tests of thermal alkaline hydrolysis of sludge showed that proteins in sludge were clearly hydrolyzed but the hydrolysis of proteins was not clearly affected by alkaline strength.Protein contents in the original sludge,the residous from hydrolysis with pH13.93 strength and the residous from hydrolysis with pH14.33 strength were 42.25 g/kg,11.6 g/kg and 11.5 g/kg,respectively.As the alkali concentration increased,contents of heavy metals except arsenic in the hydrolysis residouses was increased.As compared with the original sludge,the residous from hydrolysis with pH14.33 strength enriched Ni,As,Cd,Zn,Cu,Cr,and Pb by 78.69%,-65.13%,119.32%,107.50%,110.61%,144.77%and 115.07%,respectively.The hydrolysate with pH13.93 strength and the hydrolysate with pH14.33 strength contained 4 g/L and 6 g/L of amino acids,29.8 g/L and 36.5 g/L of total organic carbon,2.1 g/L and 3.1 g/L of total macro-nutrients(N+P2O5+K2O),3.7 mg/L and 3.4 mg/L of micro-nutrients(Fe+Mn+Cu+Zn),respectively.2.Results from experiments of solid-state fermentation of Trichoderma guizhouense NJAU4742 and rice straw with addition of sludge hydrolysates showed that the effect of sludge hydrolysates on sporulation was depended on volumes of the hydrolysate added to the fermentation substrates.The sludge hydrolysate in a level of 2%(v/w)of fermentation substrates enhanced the NJAU4742 sporulation with the highest spore yield 8.57 X108 CFU·g-1 after 7 d of solid state fermentation.3.Results from cucumber soil pot experiment with addition of fermented extracts showed that the effect of fermented extracts on cucumber growth was depended on amount of the sludge hydrolysates added into the fermentation.The fermented liquid(treatment T3)from fermentation with sludge hydrolysate at 2%(v/w)of fermentation substrates significantly enhanced the growth of cucumber.As compare with control of no hydrolysate,the treatment T3 increased the stem diameter,SPAD,plant height,above-ground dry weight and below-ground dry weight of cucumber by 71.32%,58.19%,93.76%,60.61%and 69.55%,respectively;the treatment T3 increased the stem diameter,leaf area,SPAD,plant height,above-ground dry weight and below-ground dry weight of Chinese cabbage by 64.18%,63.53%,38.43%,76.03%,115.38%and 117.59%,respectively.Fermented extracts from addition of more than 4%(v/w)of sludge hydrolysate to the substrate weight negatively affect(P<0.05)growth of both cucumber and Chinese cabbage(P<0.05).In conclusion,application of the thermal alkaline hydrolysis technology in treating excess sludge from city domestic wastewater treatment plant can enrich heavy metals(not including arsenic)into the residouses of the hydrolysis.This makes possibility to recycle the hydrolysates,which are rich in organic substences.Addition of sludge hydrolysates in proper amount can promote the spore yield of Trichoderma in solid state fermentation.The extracts from the fermentation added with proper amount of sludge hydrolysates can significantly enhance growth of cucumber and Chinese cabbage.More furthor efforts are needed to study the processes in detoxifying and recycling of excess sludge.