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.