Studies On Composting Technology Of Large Scale Farm Dairy Manure

Huge amount of dairy manure from large scale dairy cattle farm without being treated timely, brings serious environment problems. Composting is an important technology to process and to resource recovery animal manure, so it is of great significance to improve compost processing efficiency and product quality in order to spread composting to be used wildly. In view of the characteristics of high water content of the dairy manure, it is uneconomical to management it by composting. With the starting point at the harmless and reclamation of dairy manure,in this paper,using dry grinded maize straw as compost amendment mixed with pre-mentioned dairy manure to compost under a relatively high initial water content(65%～80%). This paper studied on: (1), the effect of different initial water content, different between two composting system(the forced aeration static bed composting system and rotating aerobic static in-vessel composting system) and air-drying dehydration as pre-treatment on changes in physico-chemical parameters during composting; (2), effect of different composting treatments on changes in contents of plant nutrition ingredients, such as N, P, K and humus; (3), effect of different composting treatments on changes in total and DTPA-extraction contents of heavy metals (Cu, Zn, Pb, Cd). The experiment results showed that:(1) All composting treatments were able to rise the composting temperature to the thermophilic stage quickly, and maintained 8 to 12 days above 50℃, which was enough to satisfy the requirements of sanitary standard for the harmless (GB7959-1987). Not only did the treatment using air-drying dehydration as pre-treatment save the composting cost because of decreasing the requirement of amendment, but also cut down the time of composting stability, improved the compost efficiency. At the end of composting, the compost bulk density (dry) increased, meanwhile, the volume of composting pile declined to about half of initial volume. So the experiment obtained good reducing quantity.(2) After the composting, the water content of all treatments declined below 40%, obtaining effective anhydration; the pH value increased significantly in the decomposition stage; than declined to weak alkaline range in the following stage of composting until compost maturity by the large. But at the thermophilic stage, relatively high pH value also caused great N-losses. In all of the treatments studied, there was an increase in the EC. At the end of composting, the organic matter was lost up to 60% of initial value; the C/N ratios declined below 20; WSC contents all decreased less than 16g·kg-1; the NH4-N contents went down at the end of composting until it reached values below 0.4g·kg-1 of dry matter; all treatments NH4-N/NO3-N were below 0.5 except treatment using forced aeration static bed composting system with initial water content 65% (NH4-N/NO3-N﹥3), indicated that this treatment was not maturity very well. By the GI test, all treatments GI was above 50% at the end of composting; moreover, treatments using forced aeration static bed composting system at relatively high water content and composting with air-drying dehydration as pre-treatment obtained higher GI up to 80%, eliminated the phytotoxicity basically.(3) During the composting, the TNW and TKNW contents fluctuated greatly, slightly less than their initial contents; the contents of TN, TP, TK, Avail-P and Avail-K increased respectively; following the composting progress, there was an increase in humus carbon and humic acid carbon; in the contrary, there was a decrease in fulvic acid carbon; moreover, in the experiments, the higher water content in composting maturity stage, the higher obtained the composting humification index(HI); compared to the initial values, there was a slightly increasing in heavy metal(Cu, Zn, Pb) contents and DTPA-extraction contents, however, the percentage of DTPA-extraction contents in heavy metal total contents was decreased significantly. Therefore, the bioactivity of heavy metals(Cu, Zn, Pb) were reduced by composting.Using dry maize straw polishings as compost amendment to process high water content dairy manure by composting, at a high initial compost water content(70%～80%), while by means of proper process conditions such as ventilation and turning, the composting progress went well and achieved the aim of harmless and resource recovery. It is better to compost of dairy manure and dry grinded maize straw at relatively high initial water content in static bed system to benefit the compost maturity process. It is cost effective and efficiency to compost directly with the dairy manure of air-drying dehydration pre-treatment which could reduce the amount of compost amendment and improve the composting process.