Compost heat recovery in fish ponds data

Low ambient temperature is a natural occurrence that takes place every night and also during certain seasons of the year. In addition, low temperature extremes can occur due to climate change. This low ambient temperature results in low temperature of water bodies which in turn lead to reduced activity, feed intake and eventually growth of warm water fish species. Various technologies such as greenhouses, solar heaters and electrical heaters have been introduced to increase pond water temperature for fish culture but they are out of reach to most resource poor fish farmers. Therefore, this study explored the viability of aerobic composting as an alternative method to heating up of fish ponds with the added ecosystem service of producing compost. The first research hypothesis of this study was that the type of manure used during composting does not have an effect on the compost quality and heat generation of the compost. The second research hypothesis was that compost heat cannot sufficiently heat up fish pond water. Twelve fish ponds measuring 0.96 m length x 0.86 m width x 0.71 m height were constructed using wood planks, lined with polythene and each filled with 250 liters of water. Aluminum containers measuring 0.5 m length x 0.5 m width x 0.5 m height were floated in each pond and filled randomly with a mixture of either cattle manure + maize stovers + water, chicken manure + maize stovers + water, or water only (control). Therefore each treatment and control was replicated four times in a completely randomized design. All the mixtures of manure + maize stovers + water attained a Carbon: Nitrogen (C: N) ratio of 30:1 and moisture content of 65%. The compost was turned daily for 21 days by emptying the contents of the floating aluminum container into a second aluminum container which was then floated on the fish pond water. Measurements of compost pH, compost heat at 5, 10, 15, 20 and 25 cm depth, and water temperature were done at 8 am, 12 pm and 4 pm daily using a pH meter and thermometer probes. Data that were collected at different times of the day and/or different depths (compost) were averaged before analysis. In addition, a comparison was done for compost temperature at 5 cm (surface) and 25 cm (core) depths for the two manure types. The results showed that the composting cattle manure attained higher temperatures (especially at 5 cm depth) compared to the composting chicken manure but the latter heated the fish pond water better. This was attributed to the high level of lignin in the composting cattle manure. It is resistant to degradation (composting) and therefore enabled penetration of air into the composting mixture which not only increased heat generation by aerobic micro-organisms but also led to heat loss to the air and therefore low heat transmission to the water through the aluminum container. It was concluded that both manure types can be used to make larger piles of compost for improved heating up of fish ponds.环境低温是一种自然现象，每日夜间及一年中特定季节均会出现。此外，气候变化亦可能引发极端低温事件。此类环境低温会导致水体温度降低，进而使温水性鱼类的活动量下降、摄食量减少，并最终抑制其生长发育。当前已有温室、太阳能加热器及电加热器等多种技术被用于提升养殖池塘水温，但多数资源匮乏的养鱼户无力负担此类设备。为此，本研究探索了好氧堆肥技术作为池塘增温替代方案的可行性，同时可附带产出堆肥产品，兼具生态服务价值。本研究的第一项研究假说为：堆肥过程中所用粪肥的类型，对堆肥质量及堆肥产热效率无显著影响。第二项研究假说为：堆肥产生的热量不足以有效提升养殖池塘的水温。本研究采用木板搭建了12个养殖池塘，规格为长0.96米×宽0.86米×高0.71米，池塘内壁衬有聚乙烯薄膜，每个池塘注入250升水体。每个池塘内漂浮一个规格为长0.5米×宽0.5米×高0.5米的铝制容器，容器内随机填充以下三种物料之一：牛粪+玉米秸秆+水、鸡粪+玉米秸秆+水，或仅加水（对照组）。本试验采用完全随机设计，各处理组与对照组均设置4次重复。所有粪肥+玉米秸秆+水的混合物料均调整至碳氮比（Carbon: Nitrogen, C:N）30:1，含水率65%。堆肥过程每日翻堆一次，持续21天：将漂浮铝制容器内的物料转移至第二个铝制容器，随后将该容器重新漂浮于池塘水体之上。每日早8点、午12点及晚4点，使用pH计及温度探头分别测定堆肥pH值、堆肥在5、10、15、20及25厘米深度处的温度，以及池塘水温。每日不同时段及不同堆肥深度采集的数据，在分析前均进行均值处理。此外，本研究还对比了两种粪肥堆肥在5厘米（表层）及25厘米（核心层）深度处的温度。研究结果显示：牛粪堆肥的温度更高（尤其在5厘米深度处），但鸡粪堆肥对池塘水温的提升效果更佳。该现象归因于牛粪堆肥中木质素含量较高：木质素难以被堆肥降解，因此空气可顺利渗透进入堆肥混合物，这一方面通过好氧微生物的活动提升了产热效率，另一方面也使得部分热量散失至空气中，最终通过铝制容器传递至水体的热量相对较少。综上，两种粪肥均可用于制备大体积堆肥，以更高效地提升养殖池塘水温。