Bio-Filtration Technologies for Filtering Ammonia in Fish Tank Effluent for Reuse—A Review
Grism Obeti, Lawrence
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Peri-urban fish farms with limited access to open natural water bodies draw fresh water from urban water supply and dug wells, which is unreliable and costly. Reuse of fish pond effluent is also limited by high ammonia concentration (> 0.3 mg/L) that renders water toxic and is stressful to fish. Despite the existence of several fish effluent treatment methods, not all may be appropriate for a particular location. This review article therefore examines the various fish effluent treatment methods to aid selection of the most suitable one(s) for peri-urban areas. The key parameters considered in their comparison were: initial, operational and maintenance costs; ammonia removal efficiency; energy consumption and land requirement. The effluent treatment methods are both conventional and non-conventional. Despite a slight higher treatment efficiency and less space requirement by conventional methods, they mainly require reliable power supply for continuous running, highly skilled labor for operation and maintenance leading to high operational costs. In addition, their investment costs are higher than non-conventional methods, hence not widely applied in developing countries and majority have broken down. On the other hand, non-conventional methods such as constructed wetlands are widely in use for treating effluent mainly due to their cost effectiveness and no or little energy requirement. Constructed wetlands were found most suitable bio-filtration system for treating fish effluent because they are cost effective, require less skilled labor and still have better effluent treatment though space required is slightly more. Vegetables (lettuce, collards, etc.) have potential to grow in constructed wetlands thus form vegetable-based bio-filtration units which serve not only as bio-filters but also provide additional sources of nutrition and income. This review indicated limited information on the appropriate size and performance of vegetable-based bio-filtration unit utilizing indigenous vegetables and recommended further research to explore the idea.