| SUMMARYWater quality deterioration due to excessive nutrient loading in aquaculture production systems is of great concern not only as it relates to the water quality requirements of the cultured animals but also to the quantity and quality of waste discharged from these systems. There is a growing global consensus that one of the critical goals for aquaculture farming is to develop cost-effective production systems with minimal net discharge of wastes into receiving environments. As the fish quantity increases, feed input and subsequent waste products increase, causing a deterioration of the water quality in the system. The demand for high quality water and the disposal of effluent are often the first set of constraints that must be successfully satisfied by designers of aquaculture production systemsConventional wastewater treatment systems are costly to install and to operate. This work investigates the potential of an alternative reliable system. The objective of this study is to assess a conceptual layout for an inexpensive and simple system that can treat aquaculture wastewater discharge to acceptable standards. The main reason for treating solids discharged from aquaculture systems is to reduce potential negative impacts on the surrounding aquatic environment. Biological control by algae and bacteria has so far been the most economically feasible approach. However, little work has been carried out on a botanical approach to the treatment of aquaculture wastewaters. The benefits of botanical treatment systems over conventional methods may be realized through improvements in nutrient and pollutant removal together with environmental, ecological and possible financial benefits. Therefore the ecological engineering is a response to the growing need for engineering practice to provide for human welfare while at the same time protecting the natural environment from which goods and services are drawn. Our contribution is to propose a reasonable technique for the management of aquacultural farms with the aim of establishing a sustainable production while protecting the receiving aquatic environment in the foreseeable future.A cost effective technique for treating aquaculture discharge water using the grass species, Lolium perenne Lain was developed. In this study, two systems, one a recirculating system and the other a floating plant bed system were compared for their effectiveness in the removal of harmful nutrients from the wastewater. The grass species L. perenne was used as a plant biofilter and the vegetable species Amaranthus viridis was used to evaluate the suitability of the discharge water for irrigation. Both the floating plant bed and the recirculating system performed well in terms of nutrients removal, although plant growth was not robust in the former system and the latter system is energy consuming. Treatment by L. perenne remarkably improved the irrigation water quality. A. viridis plants irrigated with the phytotreated discharge water had less concentration of heavy metals in their tissues compared to those irrigated with untreated discharge.The second step was to evaluate the potential bioremediation of aquacultural discharge using a combination of nitrobacteria culture solution and L. perenne. This study was conducted in three parts: the first part was the assessment of the effects of a floating plant biofilter when used with or without additional oxygen; the second part was to study the effects of the combination of the plant biofilter and nitrobacteria solution at different ammonia load; the third part assessed the impact of abrupt change in pH to the system stability. The influence of additional oxygen on nitrogen dynamics was noticeable and the nutrients removal rate was mainly related to the initial concentration of ammonia. Gradual increase in volumes of nitrobacteria solution resulted in an increase in the removal rate of TAN and a decrease in the time for TAN removal in the compartments with high ammonia concentration. The system showed a "buffer capacity" in maintaining the pH within a very narrow range despite the abrupt pH variations. L. perenne demonstrated ability to improve wastewater quality, although the system showed limitations in case of excessively high ammonia load.Finally, we developed an aquaculture solids management using a combination of sand/gravel or unwoven fabric bed with L. perenne as a plant biofilter. This work is an evaluation of the efficiency of a sand-gravel or unwoven fabric bed system and L perenne as plant biofilter in the reduction of solids and nutrients removal from aquaculture discharge water. The first step consisted of the collection of wastewater in the tank and the distribution at three different hydraulic loading regimes (0.5, 1, 1.5L/hour) to the different experimental systems. The second step was to evaluate the performance of the different systems. The first system consisted of a bucket filled with a substrate of sand/gravel (20cm of depth), on the bottom of which was a 80 mesh/inc~2 of nylon (S1); the second was similar, but was planted with L. perenne (S2); the third was planted with a grass plate consisting of 7 layers unwoven fabric planted with L. perenne (S3). The second system showed the best performance in reducing solids as well as in nutrients (TN, TP and COD) reduction. The removal rate for TS, TN, and TP were negatively related to the loading regimes, with 0.5L/hour being the most efficient and was thus taken as the reference. L. Perenne played an important role in wastewater eco-treatment by absorbing dissolved pollutants (TAN) as nutrients for its growth.This study pointed out some efficient and low cost management approaches that can be applied for small scale farms and low income communities in order to overcome pollution that might result from aquaculture activity. In addition, L. prenne showed the ability to mitigate the harmful effects that might be caused by high ammonia concentration in aquaculture wastewater. This plant has demonstrated potential to reduce nutrients load in aquaculture discharge water with an additional advantage of reducing the concentration of heavy metals in aquaculture discharge water and serving as a source of animal feed.
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