The natural cycle of nitrogen involves several biological and non-biological process including: mineralization, nitrification, denitrification, nitrogen fixation, microbial and plant uptake of nitrogen, ammonia volatilization, leaching of nitrite and nitrate and ammonia fixation. Nitrogen exists naturally in the environment and is constantly being converted from organic to an inorganic form and vice versa. Production of commercial fertilizer adds up to the natural source of nitrogen. The main source of nitrogen include: atmospheric precipitation, geological sources, agricultural land, livestock and poultry operations and urban waste. Agricultural emissions show a strong increase due to the application of fertilizer to agricultural soils, grazing of animals and spreading of animal manure. Emissions from agricultural practices and animal manure wastes are the major source of nitrogen pollution in surface and underground water. Soil erosion and runoff from fertilized land as well as domestic and industrial wastes contribute to the enrichment of lakes and streams with nutrients. Nitrates concentration exceeding certain limits in drinking water is toxic to animals and humans, especially infants. Nuisance of algal bloom and fish kills in lakes and rivers occurs due to eutrophication. Obnoxious colours and smells are developed as a result of organic matter decay and are destroying the natural beauty of the environment. The water born contaminants affect human health from both recreational use of contaminated surface water and from ingestion of contaminated drinking water derived from surface or ground water sources. The methods for abatement of nitrogen pollution must follow multi pathways. First, the source and amount of pollution must be detected and defined. Second, the possible ways to treat animal and domestic wastes should be carefully investigated. Third, better agricultural practices should be developed that include: proper storage and application of slurry and solid manure, rapid incorporation of slurry and solid manure into the soil, use of band spreading machineries such as trailing house and trailing shoe and sub-surface applicators, use of specifically made round covers fitted to above ground tanks and slurry lagoons, applying fertilizers during periods of greatest crop demand at or near the plant roots in smaller amounts with frequent applications, using multiple cropping systems such as using crop rotations or intercropping to increase the efficiency of nitrogen uses and changing current livestock production techniques.

Fish proteins are found in the flesh, head, frames, fin, tail, skin and guts of the fish in varying quantities. Unutilized fish and fish processing waste can be used to produce fish proteins which contain amino acids and many bioactive peptides. After removing the fish flesh during the fish processing operation, all other parts are considered wastes which are not properly utilized. The aim of this study was to evaluate the enzymatic extraction of protein from mackerel fish processing waste. Enzymatic extraction of proteins was carried out using alcalase enzyme at three concentrations (0.5, 1 or 2%) and four hydrolysis times (1, 2, 3 and 4 h). The fish protein hydrolysate was dried using a spray dryer to obtain protein powder. The highest protein yield (76.30% from whole fish and 74.53% from the frame) was obtained using 2.0% enzyme concentration after 4 h of hydrolysis. The results showed that increasing the enzyme concentration from 0.5 to 2% (400%) increased the protein yield by 3.13-43.52% depending upon the fish part and reaction time used. Increasing the enzyme concentration by 4 fold for a small increase in protein yield may appear unjustified. Therefore, the enzyme concentration of 0.5% should be used for the protein extraction unless the enzyme is recycled or an immobilized reactor is used in order to reduce the cost associated with the enzyme. Also, increasing the hydrolysis time from 1 to 4 h (400%) increased the protein yield by 16.45 -50.82% depending upon the fish part and enzyme concentration used. Increasing the hydrolysis time by 4 fold for a small increase in protein yield will increase the capital and operating costs of protein production. A shorter hydrolysis time will allow more throughput and/or reduce the volume of the reactor thereby reducing the cost of protein extraction. Therefore, a 1 h reaction time for protein extraction is recommended. The results showed that the combined fish waste can be used for protein extraction without any segregation.

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