Study On The Shearing-extracting Integrated Process Of Nanoscale Humic Acid From Sewage Sludge Compost And Its Agricultural Performance

Gases emission(odor and greenhouse gas)and the instable compost quality offset the environmental and economic benefits of composting,respectively.This study was carried out based on carbon conservation and development.Sewage sludge and corn stalks were chosen as the composting materials.Effects of operational conditions and indigeneous additives on gas emissions and humification process of composting were investigated.Compost produced under the optimal conditions was then used for the extraction of nanoscale humic acids.Effects of extraction parameters on the physicochemical properties and agricultural values of nanoscale humic acids were elucidated.Finally,an integrated process for simultaneous production of compost and its nanoscale humic acid was established for economic assessment.The main results were as following:(1)Aeration rates could significantly affect the compost humification process and gas emissions.Composting under the moderate aeration rate(0.24 L·kg-1DM·min^-1)could significantly increase the humic acid content and humic acid to fulvic acid ratio.Composting under low aeration rate(0.12 L·kg-1DM·min^-1)could reduce NH3 emission.However,it could increase the greenhouse gases emission.Composting under the high aeration rate(0.36 L·kg-1DM·min^-1)could slow down the degradation rate of organic matter.(2)Composting additives could slightly affect the humification process,but the effect was not significant.The addition of superphosphate and phosphogypsum could reduce NH₃ and CH₄ emissions,but phosphogypsum could increase the emission of N₂O.The addition of gypsum,superphosphate,and VT inoculum could respectively reduce greenhouse gas emissions by 13.4%,44.3%,and 18.4%(7.7,25.4 and 10.5 kgCO2-eq·t-1 DM,respectively)compared with the control.Adding dicyandiamide and hydroquinone could significantly reduce N₂O emissions.Compared with no additives,an 80.2%(43.9 kgCO₂-eq·t-1 DM)decrease in greenhouse gas emissions was obtained by the combined use of superphosphate,hydroquinone and dicyandiamide.Inoculum could significantly accelerate the humification process of the composting,while superphosphate could speed up the mineralization process of the composting.(3)The nanosacle humic acid was obtained by leaching the maturity compost in alkali solution combined with high-speed shearing(shearing-extracting integrated)process.Considered the diameter of the nanoscale humic acid as the primary index,the sequences of influencing factors were:reaction time,shearing speed,alkali concentration,reaction temperature,surfactant addition amount,acid precipitation time and solid to liquid ratio.Through orthogonal test,the optimal condition was reached with 0.35 mol·L^-1 NaOH,a solid to alkali liquor ratio of 1:20(weight:volume),reaction temperature of 50?,shearing speed of 24500 r·min^-1,reaction time of 23 min,addition of 0.45%surfactant and acid precipitation time of 3.7 h.Under this condition,the average diameter of the nanoscale humic acid was below 70 nm.Compared with the common humic acid,the nanoscale humic acid had a narrow and uniform diameter distribution,and improved the heat resistance.(4)Both nanoscale humic acid and common humic acid could promote the growth of rice seedlings,and the nanoscale humic acid works better than common humic acid.The growth of rice seedlings performed best with the addition of nanoscale humic acid between 1-2 mmol C·L^-1.Humic acid products(nanoscale humic acid and common humic acid)did not cause lipid peroxidation in rice seedlings with the addition of 0.5-4 mmol C·L^-1.(5)A municipal wastewater treatment plant with the treatment capacity of 10×104m³·d^-1 and the sludge production of 150 t·d^-1 was choosen as the research object of this study.The sludge was all treated using the aerobic composting method.After composting,70%of the maturity compost was used for garden fertilizer,and other 30%of the maturity compost was used for the preparation of nanoscale humic acid.The infrastructure investments and operating costs of this process were about 18.59 million and 29.34 million CNY·yr-1,separately.The production of garden organic fertilizer and naoscale humic acid were about 14,904 t and 800 t,separately.The annual aggregate output of garden organic fertilizer and naoscale humic acid was about 43.92 million CNY.This integrated process for simultaneous production of compost and its nanoscale humic acid was an environmental friendly technology.