Design And Performance Evaluation Of Aerobic Composting Reactor

This study was based on the longer degradation fermentation time andother issuesusing straw and livestock waste, take the use of aerobic fermentation to treat solid wastein order to shorten fermentation time and increase its handling capacity.Aim at materials undermixing, insufficientaeration and incomplete fermentation and so on, an aerobic compostingreactorwas developed with the function of strengtheningradial flow. Its some properties including thermal insulation, stirring and fermentation were tested respectively. The results are as follows,(1) The reaction device includes, main structure, ventilation system, transmission system, control system. Its core is the stirrer, which each paddle has radial plectrums on the upper surface and aeration hole on the lower surface to increase the fluidity of composting materials so as to fully contact with air and enhance uniformity and thoroughness of aerobic fermentation. Sensors were set insidethe reactor to Real-time monitoroxygen concentration.(2) Thermal insulation performance:cooling temperature difference was 10.9℃ and 18.4℃ in conventional way and aeration respectively after 14.5 h, which the cooling temperature difference between conventional and stirring waywas 7.5℃. The average heat transfer coefficient of the reactorwas 1.65w?(m2?k)-1, and the average heat loss was 6.49×106J after 5 min aeration.(3) Stirring performance: variable coefficient was 41.25% after 2 min blend stirring with TS 70% hard confetti and TS 50% saw dust, and the variable coefficient was 9.59%and 7.93% respectively afterstirring 5min and 10 min, which the valueswere less than10%, showing that materials were uniform. During the fermentation, the radial plectrums can increase materials’ fluidity, enhance the contact between the material and oxygen, and accelerate fermentation so as to shorten greatlythe fermentation period.(4) The fermentation performance: the optimal ratio of 2:2:1 of dry masswas obtained after orthogonal experiment optimization of cow dung, corn stove and wheat bran. The compost experiments was carried out by the optimal raw material ratio, the appearance of materials changed from initial yellow with pungent smell to puce with stronger humus smell when fermentation was terminated. The temperature of compost maintained larger than 50℃ for 5.4daysand the highest temperature was 68.4℃. During the composting, oxygen concentration ofevery layer was higher than 8%, and the maximum standard deviation of oxygen concentration was 0.82, which the variable coefficient was 6.28%, showing that degree of deviationof oxygen concentration was smaller andoxygen concentration of every layer was uniform. The p H in every layer was changing from declining to rising, then to declining over time, and final p H reduced to 8.2 which conforms to the national bio-safety disposal processing requirements. The moisture content decreased from 66.77% to 32.92%. When the compost terminated, degradationamount of organic matter of every layers reached 14.22%, 14.89% and 13.80% respectively, final organic matter content of every layer was 76.13%, 75.45% and 76.54%, respectively. Furthermore, total organic carbon(TOC) increased from initial 1.66% to final 2.26%, final total nitrogen(TN) and C/N reduced from 44.21% to 37.68% and from 29.92 to 16.67, respectively, which met the national standard. Seed germination index(GI) of upper, middle and low layers were greater than 85% and the maximum of upper layer was 96.59% when compost ended, showing that composting products can meet application demand.The performance of reactor was comprehensively evaluated by the fuzzy mathematical evaluation model from screening evaluation factors, establishing evaluation matrix, determining fuzzy sets of membership degree of every factors, determining membership degree of each evaluation level. The results showed that weight descending order of the impact factors of reactor was u1(the integrated heat transfer coefficient)>u6(the average oxygen concentration)>u3(the duration of high temperature 50 ℃ or higher)= u4(C/N)> u7(seed germination index)> u2(mixed coefficient of variation)> u5(organic matter), among which the integrated heat transfer coefficient and average oxygen concentration were two important indexes affecting reactor performance, and organic matter content showed less effect on reactorperformance. According to the principle of maximum membership degree, the membership degree of fine grades is 0.658, indicating the reactor feasibility is better.