Background:
Aquaculture industry is processing quickly over the past few decades. This rapid growth has resulted in competition for natural resources i.e. land and water. Apart from strong annual growth, the culture of fish over the past few decades has also been strongly intensified. This intensification has significant drawbacks such as an increased environmental impact due to larger amount of waste discharged in the form of effluent. Aquaculture, like other animal‐production sector generates biological wastes but unlike other sectors, the aquatic animals cannot separate their living space from their area of excretion. This causes deterioration in water quality due to ammonical excretion inside the aquaculture production system leading to poor growth and an increase in the incidences of diseases. Management of the waste generated from aquaculture is quite difficult and costly as the waste disintegrated becomes diluted in the culture water. Treatment of wastewater demands large investment and sophisticated equipment. Feed is the main source of waste and is also responsible for most of the environmental impact of aquaculture, and water quality is a critical factor when culturing any aquatic organism. Optimal water quality varies by species and must be monitored to ensure growth and survival. The quality of water in aquaculture production systems can significantly affect the organism’s health and the costs associated. Therefore, removal of particles from water flow is important in aquaculture. Suspended solids, dissolved solids, and organic matter are removed from water by filtration of water through suitable media. In aquaculture, mechanical filtration is used primarily for the separation of solids and liquids. Concentration of ammonia in culture water is reduced by biological filtration process. Biological filters are devices to culture microorganism that will perform the given task of reducing the ammonia concentration when water with high ammonia level flows through them. In water, both Ammonia (NH3) and ammonium ion (NH4 + ) are present and their sum is known as Total Ammonia Nitrogen (TAN) and their proportions vary with pH. Ammonia (NH3) is toxic to fish and its presence in water is important in aquaculture practices. Biological filters (biofilters) are used to maintain water quality in recirculating or closed aquaculture systems. Biofilters are also used to improve the water quality before water is discharged from a facility. In biological filters, bacteria are used to convert ammonia in various steps (i) Conversion of ammonium to Nitrite (ii) conversion of Nitrite to Nitrate, and (iii) Conversion of nitrate to molecular nitrogen (denitrification). The first two steps, known as nitrification, are performed by specific bacteria which oxidize ammonia and nitrite. The autotrophic bacteria, nitrosomonas bacteria utilize ammonia as a food source and produce nitrite. This nitrite is further converted to nitrate by nitrobacter. These bacteria grow and colonize on the filter medium of biological filter. Both types of nitrifying bacteria will grow and colonize the biofilter as long as food is available. The efficiency of the nitrification process depends on the optimum growth of bacteria on the biofilter medium. One of the main factors affecting the bacterial growth is the amount ammonia in the water. Therefore, it is very much essential to develop a Biological Filter (biofilter) for better water quality and environment of aquaculture systems. In consideration with market potential for biofilter, ICAR-CIFE has developed a prototype of timer-based and power operated water filtration system for aquaculture which can be used in aquarium as well as for intensive aquaculture system. This filter will improve the water quality of the system so that growth of the fish can be better as compared to water exchange system aquaculture. In addition to this, huge water and labour cost for exchanging water can also be saved.
Technology Details:
The prototype of biofilter consists of outer (150 mm dia.) and inner casing (75 mm dia.) made up of PVC pipes. The outer casing is fabricated using 2 pieces of detachable perforated PVC pipes. The detachable upper and lower portions of outer casing are clubbed together with the help of PVC coupler socket. This arrangement provides ease in detaching the upper and lower portions for regular inspection and maintenance of biofilter. The surface of outer casing is perforated. The inner casing which holds suitable biofilter media (viz. bio-rings, bio-balls etc.) is fabricated with perforated PVC pipe of 75 mm dia. The surface of inner casing has perforations with holes of 15 mm dia. The space between the inner and outer casing is filled-up with cotton foam sponge which acts as a mechanical filter to prevent the entry of suspended solids into the system. At the top of the inner casing, a cone shaped perforated cup (75 mm dia.) is provided to prevent the entry of bio-rings (i.e. biofilter media) into the pump. The inner and outer casings are covered at the bottom and top with PVC end caps to make one unit of prototype of overall height 45 cm. A stand is provided the bottom to support the prototype to stand stable in the water body. A submersible pump is mounted on the top of the top end cap. The submersible pump is facilitated with a timer and contactor for recirculation of water at predetermined rate of water exchange at regular intervals of time