Safe disposal of waste waters has become a hot potato both in developed and developing nations. Pakistan is also standing in the row of countries facing a swift and dramatic increase in population and as a result, a massive quantity of wastewater being produced in Pakistan.
It is estimated that 975,000 million gallons per day (MGD) wastewater produced including 674,000 MGD from municipal and 301,000 MGD from industrial uses. Pakistan once had 5,300 cubic meters per capita water availability in 1947 but now it is less than 1,000 cubic meter in 2017 and going to below 600 cubic meters per capita by 2050.
All this water is being consumed for human needs including agricultural, industrial and domestic purposes. The major consumer of fresh water is agriculture sector which utilizes more than 90% of freshwater resources. Thus, considering the societal demands, environmental safety, and future sustainability, there is a dire need of tackling the challenges offered by water scarcity.
These issues could be resolved to a huge extent by re-using the waste water but the major issue is the pollution load in waste waters which make its use restricted. And only 2% of this wastewater is being treated in just a few major cities of Pakistan. The untreated waste waters or city effluents are ultimately being disposed into agricultural lands for irrigation to food crops.
Municipalities, WASA agencies and farmers of peri-urban areas are only considering the economic benefits and nutritive values of untreated wastewater but they are putting the environment sustainability on risk. In addition to this, nutritive value of wastewater is low at cost and available at vicinity, so farmers prefer to it.
But this is a blessing in disguise, the severe effects of pollutants present in the wastewater have started showing their effects in the form of a sick community full of diseases.
Continuous disposal of this wastewater without any prior treatment is causing critical pollution problems like damage to ecological systems, living resources and human health including diseases like diarrhea, kidney failure, central nervous system dysfunction, liver damage, hepatitis and water-borne diseases.
Nearly 250,000 per year deaths occur in Pakistan due to it. When this water applied to agriculture land it contaminates the soils with pollutants. Wastewater contains heavy metals including mercury, cadmium, lead, chromium and arsenic, etc., organic material such as feces, food, clothes, paper fibers, humus and plant material; Inorganic particles like metal particles, ceramics, etc., toxins including pesticides, herbicides, and poisons, etc., bacteria, viruses, protozoa, and parasites. So, proper treatments are required in order to use this water for agriculture.
Conventional approaches for the elimination of toxic matter from wastewater includes like chemical precipitation, reverse osmosis, electroflotation, membrane filtration, and adsorption upon activated carbon.
These methods encompass more capital costs, low efficiency, inadequate removal, and may be related to formation of secondary wastes which need to be treated or to safely dispose of again. In addition to not being a green technology, its high cost has prompted the quest for cheaper and comparable substitutes.
Above mentioned issues demand to discover the comparable and cost-efficient methods to treat the wastewater. It can be done in a way economical in every aspect; treatment by using biosorbents which have low cost, high sorption capacity and easily accessible.
The utilization of naturally available bio-based absorbents appears to be a novelty for this issue. It not only fulfills the water shortage but also helps in saving disposal of effluents. There are many procedures used to treat polluted water; the choice of treatment method is based upon cost of treatment and type or amount of waste waters
Adsorption process using agricultural by-products as biosorbents is a very economical and effective process. Among these, agricultural and food-industry related naturally available bio-wastes can be used as an efficient material for the removal of toxic and heavy metals from domestic sewage and industrial effluents. These by-products are a good alternative to other materials as they are sludge-free, time-saving, equally efficient, and involve small initial cost.
Due to a large number of hydroxyl groups as compared to presently used adsorbents they have an extraordinarily high affinity towards heavy metals. They also have other surplus binding sites or functional groups including carboxyl, phenolic, alcohol, amino, and ester, etc. In this respect usable biomasses to remove pollutants are tree materials like Momordi cacharantia, coconut coir pith, coconut fibres, cortex banana, hyacinth plant, dried roots, blue pine, mango leaf;
Peels including peel of various fruits (e.g. orange, chestnut shell, coconut shell, jackfruit, mosambi, lemon, pineapple), potato peel; Powder materials containing nutshell, powder of eggshell, walnut, Moringa oleifera seed powder; Crops material such as sugarcane bagasse, wheat straw, rice husk, rice husk-ash, rice polish, rice straw, cotton stalks, tea waste ; and others such material found in literature are fish scales, garden grass, feathers of bird, hazelnut, human hair, and pecan, etc.
Biosorbents are replacing the conventional treatments which were being used recently. Worldwide demand of biosorbents is growing at 6.2% CAGR (Compound Annual Growth Rate) and estimated to reach $4 billion by 2020. This increasing demand is due to its larger surface area, cost-effectiveness, more binding sites and better service. It is also easy to dispose of this material.
Each biomass has special sorption affinity for a certain pollutant and these can also be used simultaneously to remove a large number of toxins and pollutants present in water. Heavy metals like chromium, arsenic, cadmium, lead, copper, mercury etc and other pollutants like dyes, organohalides, perchlorate, and fluorides can be removed by this process. It is a secondary level treatment so can be performed for both agricultural and drinking purposes.
In the last decades, ample quantity of waste water is being produced due to anthropogenic activities. So in this condition, there is a dire need of awareness among industrialists and government policymakers to diffuse these innovations to harvest their benefits. It will be killing two birds with one stone; firstly, wastewater would be treated and second, it will help in recycling fresh water.
This article is collectively authored by Muhammad Umair, Muhammad Zia-ur-Rehman, and Hinnan Khalid.