Reuse of Treated Sewage Water in Irrigating Farms
Reuse of treated sewage waters has found a vast application throughout the world. Advanced technologies allow a high level of purification that diminishes health hazards. In conditions of the global scarcity of freshwater resources and the trend to sustainable use of resources, reuse of sewage water appears to be an ideal solution. However, the health impact of the remainders of chemical, organic, and biological substances in treated sewage water has not yet been clarified.
Raw sewage water contains chemicals and pathogens that can cause serious diseases. Pathogens present in wastewater include bacteria, viruses, protozoa, and helminths. Modern sewage water reclaiming facilities can eliminate pathogens below detectable level. Almost every human activity results in the discharge of chemicals in sewage systems. While water reclaiming facilities can neutralize most chemical compounds, so-called contaminants of emerging concern including endocrine disrupting chemicals and pharmaceutically active compounds are difficult to detect and monitor by commonly used equipment. Higher concentration of CECs can cause significant environmental and health problems.
Correct evaluation of hazards connected with sewage water reuse in agriculture will help to formulate strategic goals for sewage water treatment, to eliminate or mitigate possible health risks, and to relieve public anxiety. The stakeholders interested in EHIA are agricultural crop producer, agencies for environmental protection, municipalities, and the society in general.
The research as well as experience proves a relative safety of the use of sewage waters in irrigating farms under the condition of appropriate safety technique. As far as chemical contaminants are concerned, the opinions are controversial. Some studies show that fruit, leaves, and vegetable crops do not accumulate hazardous substances; others prove that the concentration of CECs in root vegetables irrigated with treated greywater is higher than the norm.
Background of the study
Reuse of treated sewage waters has found a vast application in the USA and many other countries throughout the world, such as Israel, Great Britain, China, South Africa, and others. Such factors as the lack of fresh water and the need for irrigation make water reclaiming technologies vital necessity. Advanced technologies allow a high level of purification that diminishes health hazards. In conditions of the global scarcity of freshwater resources and the trend to sustainable use of resources, reuse of sewage water appears to be an ideal solution. However, the health impact of the remainders of chemical, organic, and biological substances is an issue for concern.
Sewage water is wastewater from households including water from toilets, washing machines, etc. collected in sewage systems. Greywater is water from households except for toilet flush. In small cities and towns, rainwater drainage mixes with sewage water in one system. The idea of collecting wastewater, its treatment and further use as a source of nutrients for plants developed in the 19th century. The first sewage farm in France appeared as early as 1868. Over time, concern about long-term environmental and health effects of sewage irrigation evoked thorough screening, elaboration of water quality tests and equipment, and severance of sanitation norms and regulations.
Government legislation establishes sanitary norms and water quality standards, and control bodies ensure implementation of the norms and observance of standards in wastewater treatment facilities. In the USA, state and local bodies are responsible for wastewater recycling standards. In 2012, 30 states and one territory adopted regulations and 15 adopted design standards or guidelines. The Environmental Protection Agency (EPA) 2012 Guidelines for Water Reuse constitute a framework for the development of standards and regulations by state authorities. Despite the variations, state regulations function are subordinated to federal laws and regulations where they concern international borders, Native American territories, multiple states. Clean Water Act (CWA) and Safe Drinking Water Act (CDWA) are primary federal laws regulating reuse of wastewater.
Currently, public opinion is increasingly sensitive to environmental issues and agrees about feasibility and sustainability of sewage water reuse. However, possible hazards for human health and long-lasting environmental effect need further investigation and explication.
Raw sewage water contains chemicals and pathogens that can cause serious diseases. Treatment of sewage water to eliminate pathogens and bind chemicals allows avoiding grave consequences. Monitoring of some contaminants had not been done until recently when research showed their increasing concentration in wastewater. Figure 1 shows contaminants of emerging concern (CEC) found in treated wastewater.
Figure 1. Categories of trace chemical constituents detectable in recycled wastewater.
Endocrine disrupting chemicals (EDC) and pharmaceutically active compounds (PAC) arouse major attention. Their concentration in treated sewage water is significantly lower than in medicines. However, there is no uniform, simple and feasible method of detecting EDC at all levels. Moreover, most water reclaiming plants do not have equipment for detecting these substances, so monitoring is problematic. Higher concentration of CECs can cause significant environmental and health problems. For example, antibiotics (penicillin, tetracyclines, and sulfonamides) build up bacterial resistance, which makes them insensitive to treatment. Disinfectants and antiseptics have toxic and biocide effect.
Pathogens present in wastewater are mainly of enteric origin. They include bacteria, viruses, protozoa, and helminths. Modern sewage water reclaiming facilities can eliminate pathogens below detectable level. However, it is worth remembering about the possibility of their presence even in treated sewage water. The probability of contracting water-borne infection depends upon the number of pathogens, their dispersion in water, the infective dose, and susceptibility of population. Diseases induced by pathogens are serious and can cause an epidemic. Bacteria convey typhoid, paratyphoid, bacillary dysentery, gastroenteritis, cholera, and other diseases. A major epidemic of cholera is unlikely because water reclaiming plants can treat bacteria effectively. However, small outbreaks have occurred due to contaminated seafood or from travelers who contracted cholera from food that they had brought in suitcases from their foreign trips. While viruses cannot multiple outside their hosts, some of them can cause severe diseases through wastewater, such as polio, hepatitis A, and viral gastroenteritis. Protozoa cause a number of diseases, where diarrhea is the main symptom, for example, giardiasis, cryptosporidiosis, or amebiosis. Parasitic worms can cause intoxication of the organism, which usually reveals through weight loss, anemia, abdominal pain, and fatigue.
A detailed assessment of environmental health impact is necessary because of several social, economic, and environmental factors. Reuse of treated sewage water in agriculture is a beneficial solution for farms because it is low-cost efficient means of irrigation and fertilizing at the same time. Sewage farms receive from wastewater effluent and farms all necessary nitrogen and much of the potassium, phosphorus, and microelements. It increases the productivity of the crops and thus the income for producers. Farm irrigation with treated sewage water solves the problem of water disposal, both in megapolises and rural areas. Sewage water from households, car washes, drainage systems, and rainfalls in smaller towns are used for irrigation instead of direct discharge in water reservoirs. In that way, farm irrigation provides an economic benefit as well as an environmental benefit. Treated sewage water undergoes extra filtration and decontamination before it soaks to waterways. Finally, reuse of the treated sewage water is one of the ways to alleviate the anthropogenic impact on nature. Instead of using scarce fresh water for irrigation and chemical fertilizers, people use sewage effluent and sludge to support crops. Nevertheless, these benefits are countered with possible negative impact on the environment and human health. Therefore, correct evaluation of hazards connected with sewage water reuse in agriculture will help to formulate strategic goals for sewage water treatment, to eliminate or mitigate possible health risks, and to relieve public anxiety. The stakeholders interested in EHIA are agricultural crop producer, agencies for environmental protection, municipalities, and the society in general.
This paper is based on the scope of knowledge of previous researchers. As there is no statistical record of health conditions resulting from the agricultural use of treated sewage waters, generalized evaluation of possible and real health impact has been done. During the preparation of this paper, legislative and technical norms were assessed to find out about the level of decontamination of sewage water.
There are several ways of disease transmission through sewage water, namely direct contact, consumption of contaminated food and water, or contact with a carrier. Respectively, risk groups include people who undergo occupational hazard while working with sewage water (in the process of collection, treatment, or irrigation), and consumers of possibly contaminated food. In irrigated agriculture, the highest possible risk of contracting a disease is by eating raw vegetables or sprayed fruit that were in a close contact with wastewater. Using sewage for irrigation of crops that undergo cooking, or are peeled before eating, or do not contact the irrigation water directly reduces the risk of infection; besides, any sprinkler-irrigated crops are considered low risk. Irrigation of pastures and grasslands with treated sewage water presents a low risk for human health as well. Minimum risk occurs in sewage water irrigation of technical crops that are not used for food, crops that undergo heat drying, crops for canning, and fodder crops. For agricultural workers, mechanized irrigation, cultivation, and harvesting minimize the risk of exposure. Long dry periods between irrigations and harvesting dried crops also reduce the probability of infection.
The research as well as experience proves a relative safety of the use of sewage waters in irrigating farms under these conditions. As far as chemical contaminants are concerned, the opinions are controversial. However, lab study of grey water irrigation effect in olive trees and vegetable crops conducted by Al-Hamaiedeh and Bino show no adverse effect as compared with control samples before irrigation. At the same time, research of Wu suggests penetration of contaminants from irrigation water into root vegetables.
Even though modern installations allow efficient treatment of sewage water from pathogens and most organic and chemical contaminants, the possibility of their residual presence in the treated sewage water remains. Therefore, the population should follow general sanitary rules and regulations.
In the United States, the level of water quality control is high. Due to this fact, there have been no significant outbreaks of cholera, typhoid, or other water-borne epidemics recently. However, research shows that the problem of sewage and wastewater reclaiming demands closer attention. Recommendations for the maximization of the health gain and minimization of health loss cover several overlapping areas. The first and the foremost is the observance of sanitary rules by the population. Trivial hygiene, washing hands, fruits and vegetables eliminate many hazards caused by pathogens and chemicals. Peeling, heat treatment and heat drying of fruit and vegetables have proved their efficiency for water-borne disease prevention.
The second recommendation concerns rules for agricultural workers engaged in irrigation with treated sewage water or working of irrigated fields. Mechanization of processes, wearing protective clothes, and observance of private hygiene after working will protect them from possible negative health impact.
The third line of recommendations concerns monitoring of CECs in the treated wastewater. Special attention should be paid to the means of detection and possible elimination of CECs. After elaboration of such equipment and its implementation, competent government bodies should revisit and update water quality standards.
Fourth, crop producers should apply irrigation treated sewage water only for technical crops that are not grown for human consumption, such as cotton, rapeseed, sisal, flax, etc. or crops that are not consumed in the raw state, such as potatoes, red beets, etc.
It would be desirable to unite global efforts in order to reach uniform standards for reclaiming of sewage water and its agricultural application. The issue under consideration relates to the problems of sustainability of global economy and global environmental protection. Therefore, it is logical to unite efforts, knowledge and technologies of various nations. The practice of reuse of sewage effluent and sludge in irrigating and fertilizing is common practice all over the world. However, in 2002, only Spain, Italy, and France of all European countries had accepted guidelines for wastewater reuse. Some countries were contemplating such regulations, and others, even the most advanced ones, had no guidelines regulating the issue.
Monitoring and evaluation
The absence of reliable statistical record impedes conducting effective an environmental health impact assessment (EHIA). Only a clear link between water-borne diseases and irrigation with treated sewage water can prove its direct negative impact on human health.
Future monitoring of real health impact should take into consideration several aspects. First, regular monitoring of treated sewage water should determine the presence of pathogens and chemical agents and their concentration. Second, scientists should pay closer attention to the seasonal character of water-borne diseases; it can indicate connection between sewage irrigation and outbreaks of diseases. Mapping of such outbreaks can also link geographical connection between sewage farms and focuses of epidemics.
The current state of knowledge allows eliminating most contaminants from sewage and wastewater. Information about real health impact of such irrigation is not consistent and requires further research. Obviously, treated sewage water is a valuable source of fertilizing for crop production and means for saving freshwater resources. Therefore, carrying out water quality research on a higher level is crucial for reduction of health hazards. At the same time, public health monitoring focused on the occurrence and spread of water-borne diseases in connection with treated sewage water irrigation would provide empiric information about real health hazards of this practice.