Introduction There are mainly two types of environmental standards: (i) quality or ambient standards for environmental media such as air, water and soil and (ii) discharge standards (i.e., emission standard for air pollution and effluent standard for wastewater) that regulate pollution released to the environment. However, there is common confusion about which type of standard to comply with even among professionals. Adoption of improper standards can make compliance more difficult for developing countries that often lack the required technical capacity and financial resources. A differentiated approach to discharge standards offers a cost-effective solution that could help improve environmental quality, such as water and air. Environmental Quality Standards vs Discharge Standards Environmental quality or ambient standards The environmental quality or ambient standards define the level of environmental state in order to guarantee a basic environmental quality for all persons and living resources. The numeric concentration value of their parameters is derived primarily from scientific, medical and epidemic research for human health and biomes (e.g. for air quality), and eco-toxicology and susceptibility tests for aquatic life (e.g. for water quality). As a result, ambient standards are universal. Hence, developing countries can use them directly and have introduced ambient standards from developed countries, especially those that share similar climatic zones and geographic features. This can help developing countries avoid repetition in investigation, expensive research, and need for verification. For example, due to its lack of capacity and resources, the People’s Republic of China (PRC) has established its ambient standards since early 1980s mainly by adopting those from Europe, Japan, the former Soviet Union, and the United States. Many countries have also increasingly aligned their ambient standards with international environmental quality standards, such as the World Health Organization’s air quality targets, as citizens demand a better living environment. Many countries have classified ambient standards, especially those of surface water, based on their intended usage. For example, Indonesia, PRC, and the Philippines categorized surface water quality standards in descending order under the following classes: for drinking and protected area, as drinking water sources with conventional treatment, for recreational and other uses with direct body contact, for irrigation and agriculture, and other uses. Discharge standards Discharge standards regulate the maximum level of certain pollutants that can be released. Regulators refer to such criteria when checking and managing pollution, while polluters must comply with them. In developed countries, these standards are largely based on the level economically achievable by best available technology (BAT) and on the experience of other countries with similar social-economic conditions. Technology pertains not only to equipment and processes but also includes techniques and operational practice. The US Environmental Protection Agency (EPA) defines pollution control technologies as best conventional technology, best practicable technology currently available, and BAT. The first two are self-explanatory. The definition for BAT is still vague but commonly understood as: Best: most effective and efficient, marginal cost is equal to marginal benefit, resulting in overall least cost to society as a whole. Available: generally accessible, but not necessarily in general use yet. Therefore, complying with discharge standards based on BAT will require reasonable effort, including technical and financial resources, from polluters. Even the US EPA only issued pollution limits achievable by best practicable technology currently available (not BAT) as national guidelines for federal states to develop and enforce their own effluent standards and discharge permit. The same approach has been used in Japan, while the PRC largely copied from the former Soviet Union in the 1980–1990s, and with it, the tradition of “strict standard but lax enforcement.” As discharge standards are underpinned by economic consideration, these can vary across countries more than environmental quality or ambient standards. This is because different social-economic development levels lead to different BAT and thus discharge standards, which in turn can greatly impact the affordability of pollution control and cost of compliance. If polluters fail to meet discharge standards even with reasonable effort, they usually do one of the following: i) shut down the pollution treatment behind the back of regulators, ii) dilute effluent intentionally or unintentionally, or iii) give up pollution control. These actions have worsened water quality despite stricter discharge standards or regulators having more resources. Even rich countries could not afford to monitor every major polluter all the time despite having online devices, much less so for developing countries. Benefits of the Differentiatiated Approach Most countries differentiate their effluent standards (i.e. a term often used for discharge standard for liquid or wastewater) according to types or sources of wastewater. Some also differentiate based on where the wastewater will be discharged—directly to the environment or into a sewer connected to a centralized or municipal wastewater treatment plant (WWTP), such as Cambodia. Viet Nam only distinguishes between discharging to waters used as drinking water sources and the rest. Not many countries further differentiate their effluent standards based on the quality of water that receive them, like PRC and the Philippines. Water bodies in classes/zones that require lower water quality, e.g. those for industrial and agriculture use, can tolerate less strict effluent limits. Meanwhile, those in the cleanest classes/zones that are used as drinking water sources or located within a protected area do not allow any discharge, as in the PRC. Supported by science, a differentiated approach has several benefits. First, it can overcome the lack of technical capacity and resources of individual polluters, especially smaller ones common in developing countries. They will just need to meet the discharge limits for releasing into sewer. These limits are usually less strict than those for direct discharge to the environment. Combined with the economy of scale of municipal or centralized WWTP linked to the sewer, it is also a more cost-effective. However, many developing countries do not have municipal WWTP yet or are still in the process of building it. This is one of the reasons why some countries have less finely classified discharge standards. Second, this approach can discourage the practice of diluting the discharge and thus, save water and foster cleaner production practices. Undiluted discharge is further desirable for WWTPs (either centralized or onsite) as they perform better at higher wastewater concentration with less energy used per unit pollution reduction. Recommendation Developing countries should classify their ambient and discharge standards to more levels according to primary uses and correspond them to each other. Effluent standards should be broken down based on the quality of receiving waters and their designated usage, utilizing the self-purification of surface water (through degradation, hydrolysis, etc). The numeric limits in these standards should first follow what is economically achievable by the best practicable technology currently available. As a country develops, it could then set limits according to BAT. They can introduce such standards by borrowing from countries with similar circumstances and adapt these measures to their own context gradually. With population and economic growth, the water quality of a river/lake or air quality of a city can still worsen even if most polluters in the watershed or airshed comply with the discharge standards. The first response is naturally to tighten the discharge standards but this often does not improve environmental quality even after a few years. This is because the total pollution load discharged to the water body or airshed is beyond its assimilative capacity to absorb and degrade. Therefore, total pollution load control is needed as well. Environmental authorities in developed countries like the United Kingdom and the US require compliance both in concentration and total pollution load for a certain period when issuing a discharge permit, in order not to exceed the carrying capacity of the receiving environment. Environmental Impact Assessment (EIA) approval in Indonesia and the PRC requires similar estimation of pollution load, in addition to discharge concentration, and demonstration of compliance in both. However, the total load control has mainly tackled point sources pollution, as evident in the limited improvement in environmental quality. In the PRC, studies and monitoring reveal that water pollution comes more from nonpoint sources such as agriculture run-off than point sources like urban sewage and industries, roughly at a 2:1 ratio. Even multilateral development banks noticed such a situation after years of investing in WWTPs. In recent years, the World Bank adjusted some of its projects’ objectives from improving a river’s water quality to reducing pollution load discharged into it. Therefore, a more holistic approach is needed, beginning with an analysis of pollution sources beyond point source pollution. Resources Government of the People’s Republic of China, Ministry of Ecology and Environment. 1998. Integrated Wastewater Discharge Standard. GB8978-1996. Government of the Philippines, Department of Environment and Natural Resources. 2016. Water Quality Guidelines and General Effluent Standards of 2016. Government of the United Kingdom, Environment Agency. 2019. Waste Water Treatment Works: Treatment Monitoring and Compliance Limits. Accessed August 2023. Government of the United States, Environmental Protection Agency. 2000. US EPA National Effluent Guidelines: The Centralized Waste Treatment Point Source Category. Code of Federal Regulations: 40 CFR. Part 437. Accessed August 2023. J. Zhang et al. 2022. Analysis on Common Problems of the Wastewater Treatment Industry in Urban [People's Republic of China]. Chemosphere. 291 (2). Accessed August 2023. Ask the Experts Xin Ren Senior Environmental Specialist, Office of Safeguards, Asian Development Bank Once an ADB safeguard reviewer, Xin Ren now works on environmental issues in rural sector. Prior to ADB, she worked at World Bank on environment in diverse sectors. She also worked at UNEP and in the People’s Republic of China on waste management and clean production, and at UNFCCC on climate change. 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