猪粪堆肥过程中养分和重金属含量的动态变化

Dynamic changes of nutrient and heavy metal concentrations during swine composting

【目的】规模化、集约化畜禽养殖业饲料中,存在滥用或超剂量使用微量元素如Cu、Zn、Fe、As添加剂的现象,导致畜禽粪便以及以畜禽粪便为来源的有机肥重金属的积累。研究堆肥过程中养分和重金属含量的动态变化,对于畜禽粪便有机肥产业的可持续发展具有重要意义。【方法】鲜猪粪在阴凉通风处风干到含水率在60%左右,用于进行55天的好氧堆肥。猪粪∶砻糠比例为6∶1 (鲜重)混匀,每周翻堆一次,每天测定温度,分别在堆肥第1、13、23、28、41和55天的上午10:00—11:00,取样测定含水量、pH值、全氮、总有机碳(TOC)、全磷、全钾以及Cr、Cd、Cu、Mn、Ni、Zn、Pb、Hg、As总量和有效态Cu、Mn、Zn含量。【结果】1)随着堆沤进程的延长,全氮先升高再下降,其峰值出现在第23～28天,之后缓慢下降;全磷与全钾逐渐升高,其峰值均在第41天、之后趋于稳定;TOC不断减少,28天以后趋于平稳。C/N先下降,第23天以后保持稳定,堆肥结束时维持在15.12、达到腐熟要求。2) 9种金属元素的总量变化各不相同,含量分别为Cr6.99～10.43 mg/kg、Cu 106.01～120.81 mg/kg、Mn 663.51～899.48 mg/kg、Ni 11.32～20.67 mg/kg、Zn1245.18～1552.13 mg/kg、Pb 0.09～0.56 mg/kg、As 0.58～1.25 mg/kg,Cd、Hg未检测出。Cr和Ni先下降、升高、再下降直至平稳,其峰值均在第23天,第28天以后趋于平稳。Cu、Mn和Zn不断升高到后期显著升高、其峰值均在第41天。As先下降再升高、在第28天以后基本平稳。Pb总体是下降,在第13天和23天其含量分别比第1天显著下降61.22%和81.63%,在第41天以后其含量未检出。有效Cu、Mn、Zn的含量远低于元素总量,分别在2.35～5.79 mg/kg、17.82～20.28 mg/kg和47.39～70.29 mg/kg。有效Cu、有效Zn总体先升高、再下降直至平稳,峰值都在第13～23天,第28天显著下降但是此后基本平稳。有效Mn总体变化不大,只在第41天显著上升。3)有效Cu与有效Zn、有效Zn与有效Mn之间呈极显著正相关关系。全钾、全磷、Cu、Zn、Mn与TOC之间呈极显著负相关关系(P <0.01),说明全钾、全磷、Cu、Zn与Mn含量的升高由堆肥过程中有机质的矿化引起。而有效Cu、有效Zn、有效Mn与TOC不存在相关关系。【结论】从23天到28天,高温的平均温度和持续时间符合畜禽粪便无害化的要求,C/N和全氮都维持在相对理想的水平,大量元素、微量元素和重金属含量基本达到稳定,表明28天是堆肥腐熟的关键时间节点。

【Objectives】Abuse of additives containing micro-elements are often happened in the feeds of intensive animal farming, which results in the accumulation of heavy metals in animal manure and the commercial organic fertilizers based on these feces. The dynamic changes of nutrient and heavy metal contents during composting were studied for the safe production of organic fertilizer.【Methods】Swine manure was mixed with rice chaff in ratio of 6∶1 (fresh weight) and then aerobically composted for 55 days. The compost piles were turned over every week for aeration. Temperatures inside the composting piles were determined every day, and compost samples were collected at PM 10:00-11:00 since 1, 13, 23, 28, 41 and 55 days, respectively. The moisture content, pH, the total concentrations of N, organic carbon (TOC), P, K, Cr, Cd, Cu, Mn, Ni, Zn, Pb, Hg and As, and the available contents of Cu, Mn and Zn were measured.【Results】1) Total N, total P and total K contents were generally increased during the composting. Total N was firstly increased and reached maximum from 23rd day to 28th day, then started decreasing. Total P and total K contents were kept increased during composting, and reached their maximum values at the 41st day. The TOC content was gradually decreased and kept stable after 28th day. The C/N ratio was deceased firstly, and then kept stable after the 23rd day, and the final C/N ratio was 15.12. 2) The total concentrations of 7 heavy metals were as flows: Cr 6.99-10.43 mg/kg, Cu 106.01-120.81 mg/kg, Mn 663.51-899.48 mg/kg, Ni 11.32-20.67 mg/kg, Zn 1245.18-1552.13 mg/kg, Pb 0.09-0.56 mg/kg and As 0.58-1.25 mg/kg. Cd and Hg were not detectable in the composts. Cr and Ni exhibited a way of decrease, increase, then decrease, till got to a stable level. The maximum contents of Cr and Ni were observed on the 23rd day and then did not significantly change after 28th day. Cu, Mn and Zn contents gradually increased, and reached maximum values on the 41st day, though a slight decrease on 55th day. As content was decreased at the beginning then increased and got to a stable level after 28th day. Pb content was decreased by 61.22% and 81.63% at the 13th and 23rd day, respectively, and was not detectable after 41st day. The available Cu, Mn and Zn contents were in the ranges of 2.35-5.79 mg/kg, 17.82-20.28 mg/kg and 47.39-70.29 mg/kg, respectively, far below their total contents. The available Cu and Zn contents exhibited the maximum from 13rd day to 23rd day, and the afterward decreases were significant after the 28th day and kept stable till the end of composting. The available Mn content was generally stable during the whole composting, except an apparent increase at 41st day. 3) Strong positive correlations were found in available contents between Cu and Zn, and Zn and Mn (P<0.01). Strong negative correlations were found between total P, total K, Cu, Mn, Zn and TOC (P<0.01), which suggested the increases in these fractions due to mineralization of organic matter during composting. However, there existed no correlations between available Cu, Zn, Mn and TOC.【Conclusions】From the 23rd to 28th day, the compost temperatures is high enough to meet the demand for non-hazardous livestock. The C/N ratio is reached ideal level and the total nitrogen content is the highest on the 28th day, The metal contents become stable after the 23rd day, except that for Mn content. Therefore, after the 28th day, the compost is matured completely and in the highest safety and nutrition level.