World population is increasing continuously and with this rising population the problem of environmental pollution is also rising rapidly. Per year a 50 % increase is being reported in the volume of the wastes which are either in the solid, liquid or gaseous form. While if we look on the other side of the picture the changing climatic conditions are resulting in continuous decline in the availability of fresh water. The per capita availability of water is declining at a rapid rate. According to the reports at the time of independence the per capita water availability in Pakistan was round about and now it has reduced to. Furthermore the agricultural lands are also facing the problems of unavailability of the proper irrigation water. The frequency as well as the severity of the drought periods is rising, thus affecting our overall crop productivity and finally the food security. It is therefore need of the hour to look for proper management of the waste water and use them for healthy purposes such as for drinking as well as for agricultural use.
As mentioned earlier the volume of the waste water is rising day by day and if it will be allowed to enter the environment untreated it is going to cause imbalance in the natural ecosystem and will also be harmful for human health. The waste water being discharged into the fresh water bodies or for agricultural utilization should contain the pollutants and other harmful substance below a specific threshold level. In this regard the remediation of the waste water is essential prior to its use for domestic and agricultural purpose. Bioremediation is the approach of using certain living organisms to absorb or detoxify the pollutants from the waste water and to make them suitable for the use by the humans and living organisms. The role of different living organisms has been exploited for this purpose. A reduction of about 80 percent in COD (chemical oxygen demand), 90 percent in BOD (Biological oxygen demand), 95% in Total viable count, 15 percent in TDS (total dissolved solids), 40 percent in phosphates, 75 percent in ammonia nitrogen, 70 percent in TSS (total suspended solids) and 4 percent in chlorides was observed by the use of Eichhornia crassipes (an aquatic plant) for bioremediation purpose. Similarly certain other living organisms such as Salvinia molesta and Ceratophyllum demersum has also been reported in certain studies for the detoxification of cadmium, chromium and other heavy metals from the waste water. Similarly the role of the certain aquatic animals such as Anodonta woodiana and Limnodrilus hoffmeisteri has also been reported for the purpose of the bioremediation. They are also involved in detoxifying the harmful heavy metals and reducing the BOD, COD, TDS, TSS and TVC etc.
The process of the bioremediation is influenced by certain physical, chemical and biological factors. Physical factors mostly include temperature, humidity, light, sediments, rainfall and turbidity. The chemical factors influencing the process of bioremediation includes BOD, COD, pH, Organic and inorganic contents along with the amount of phosphates and nitrates present. Biological factors mostly accounts for the mass of the aquatic plants and animals. The proper management of these factors is essential for successful bioremediation of waste water. The process of bioremediation usually consists of 3 main steps. The first step is the commonly known as the primary treatment which basically involves the storing of the polluted waste water in tanks and addition of various metal salts which help solids to attach with each other and form a mass at the bottom of the storage tank. This process is commonly referred as flocculation. The next step is the secondary treatment which involves the injection of the continuous air and the microorganisms in to the tanks in order to remove the remaining small solid particles. The last process commonly known as tertiary treatment involves the removal of different sort of nitrates and phosphates by the process of denitrification and chemical precipitation respectively. After this treatment the waste water can now be used successfully for irrigation purpose but in order to make it suitable for drinking purpose further processing is also required. This processing generally involves the processes of Disinfection (addition of sodium hypochlorite), reverse osmosis, filtration and irradiation.
Usman Nazir, Shakeel Ahmad Anjum, Dr. Nadeem Akbar, Imran Khan, Ayesha Farooq
Agro-biology Laboratory, Department of Agronomy, University of Agriculture, Faisalabad 38040, Pakistan