An Analytical Review of Different Approaches to Wastewater Discharge Standards with Particular Emphasis on Nutrients

A comprehensive literature and legal acts review, analysis, and systematization were conducted to identify the existing wastewater discharge standards designed for water protection against pollution and eutrophication mitigation in chosen countries. The selection of primary references has been done based on the full-text databases (Elsevier Scopus, Elsevier ScienceDirect, SpringerLink, Google Scholar, and EUR-lex) and other available publications. The choice of literature was associated with the use of a few keywords: eutrophication, wastewater treatment, phosphorus removal, nitrogen removal, nutrients, legal regulations, effluent standards, discharge requirements, etc. Within the literature review, 69 references in English, Russian, and Polish were identified as relevant for the current study.

Based on the literature and legal acts review and analysis results, various methodological approaches for setting effluent quality standards in different regions and countries were identified. Within the analysis, the effectiveness of existing legal tools, used in various countries in the field of eutrophication mitigation, was assessed to show essential methodological differences in setting the effluent quality standards in the EU Member States and the non-EU countries from different regions of the globe.

According to HELCOM recommendations, WWTPs located in the Baltic Sea catchment are obliged to comply not only with the national legal regulations but also HELCOM requirements, which have set a minimum degree of reduction and allowable values for three basic indicators: BOD 5 , TN, and TP (HELCOM 2007 ). The requirements of HELCOM, as well as EU requirements, have been developed taking into account the PE value and are constantly undergoing an amendment toward an even greater reduction of pollutant loads discharged from the treatment plants, especially the loads of nutrients (Iho et al. 2015 ; Jetoo 2018 ).

Along with the limits set by the UWWTD, stricter discharge limits were set by HELCOM ( 2007 ) in the Recommendations of the Baltic Marine Environment Protection Commission 28E/5, basing on the agreement of the Baltic Region countries Ministers of Environment in 2007.

To support the nutrient reducing actions, Denmark has introduced a discharge tax concerning BOD 5 , TN, and TP. By this tax, the “Polluter Pays Principle” has been fully adapted and obligatory for WWTPs operators. The tax rates regarding the treated wastewater discharged into receiving waters are set for three parameters: BOD 5 (2.47 Euro/kg), TN (4.44 Euro/kg), and TP (24.46 Euro/kg) using the Euro to Danish Krone exchange rate at 7.47.

The Danish legal regulations regarding wastewater discharges are one of the most restrictive in the EU countries (Brix and Arias 2005 ; Christiansen and Kardel 2005 ). The implementation of eutrophication prevention policies was pioneered by Denmark since the first discharge limits concerning municipal wastewater were established by national law in the 1960s (Klinglmair et al. 2015 ). After implementing the UWWTD, Denmark has made another step toward nutrient pollution prevention by developing more strict discharge limits (Valero et al. 2018 ). Besides the pollutants permissible concentrations, the regulations include also the recommendations on wastewater treatment technologies (Vind 2017 ).

Identifying phosphorus as the main limiting factor, conditioning the growth of aquatic vegetation, the Swedish legislation specifies the limit of TP in wastewater discharged into receivers at the level not exceeding 0.5 mg/l (Bjurhall 2004 ). Also, the 7-day biochemical oxygen demand (BOD 7 ) limit value is more restrictive as compared to the rest of the EU Member States standards and is set at 15 mg/l (Kallqvist et al. 2002 ) (about 12.5 mg/l of BOD 5 ; Öberg 2004 ). Regulations regarding the concentration of TN do not differ from those established by the UWWTD. The WWTPs in Sweden achieve a high level of phosphorus elimination mainly due to the widely used in Scandinavian countries the method of biological treatment intensified by additional chemical precipitation (Krizanac 2005 ).

In Sweden, to prevent eutrophication of lakes, the removal of phosphorus from municipal wastewater began in the 1970s (Mundt 2005 ). Currently, all water bodies in Sweden are defined as sensitive to eutrophication, which results in a unique tightening of regulations regarding the quality of wastewater discharged from WWTP.

German legislation provides the possibility for setting different national administrative regulations regarding the quality of treated wastewater, dependent not only on the WWTP capacity but also on the type and properties of the effluent receiver. In Bavaria and North Rhine-Westphalia, for example, the conditions for wastewater discharges into receivers are determined based on local administrative regulations (Henneberg and Triebskorn 2015 ). Stricter requirements are imposed on wastewater discharged into Lake Constance (ger. Bodensee) where the local limit values of pollutants in treated wastewater may differ from the German Wastewater Framework Regulation (AERZEN 2019 ). For example, the limit for total phosphorus (TP) in treated wastewater discharged into Lake Constance is 0.3 mg/l (Wilson et al. 2019 ). In this way, Germany reserves the right to establish regional effluent standards, which may be more restrictive than EU standards, and allows to take into consideration the individual characteristics of the receivers.

The AbwV establishes quality standards for five categories of WWTPs depending on the wastewater 5-day biochemical oxygen demand (BOD 5 ) load (Appendix 1 to the Regulation): cat. 1—BOD 5 < 60 kg/d (<1000 PE), cat. 2—BOD 5 < 300 kg/d (<5000 PE), cat. 3—BOD 5 < 1200 kg/d (<20,000 PE), cat. 4—BOD 5 < 6000 kg/d (<100,000 PE), cat. 5—BOD 5 < 6000 kg/d (>100,000 PE). The discharge requirements apply to ammonium nitrogen (NH 4 + –N) and total nitrogen (TN) if the wastewater temperature is above 12 °C regarding the effluent from the biological reactor of the WWTP. The 12 °C criterion may be replaced by an alternative seasonal restriction regarding the summer season—from May 1 to October 31.

The most important national regulations in the field of wastewater management in Germany are, among others, the Ordinance on Requirements for the Discharge of Wastewater into Waters (AbwV), the Federal Water Act (WHG), and other binding EU regulations.

The requirements were established for four WWTPs categories, depending on the size of the agglomeration, expressed by the population equivalent (PE), the type of wastewater receiver, and its sensitivity to eutrophication. Fifteen Member States: Austria, Belgium, Czech Republic, Denmark, Estonia, Latvia, Lithuania, Luxembourg, the Netherlands, Poland, Slovakia, Sweden, Finland, Bulgaria, and Romania have identified all their surface water bodies in their territory as sensitive areas (Zaragüeta and Acebes 2017 ). The next 13 countries: Croatia, Cyprus, France, Germany, Greece, Hungary, Ireland, Italy, Malta, Slovenia, Spain, Portugal, and United Kingdom considered only selected water areas as sensitive. After the accession to the EU, the Member States committed to the implementation of EU regulations, while the previous existing quality standards were reviewed and the legislation on the aquatic environment protection was amended.

The main legal act regulating the quality of treated municipal wastewater discharged into receivers in EU countries is the UWWTD (so-called the Wastewater Directive). This Directive regulates the level of treatment by introducing required pollutants removal efficiency in treated wastewater discharged into receivers to protect aquatic ecosystems in the Member States.

Conditions of Wastewater Discharge into the Receivers in Non-EU Countries

The states not belonging to the EU are often characterized by different approaches to establishing the legal regulations regarding the wastewater discharge into surface waters. A substantially different approach, for example, exists in the countries that were formerly part of the Soviet Union. The methodology of determining the conditions of wastewater discharge into receivers of various categories is based on the assumption, that the level of its treatment should ensure the normative water quality in the control cross-sections of individual water bodies (Neverova-Dziopak 2018). The maximum allowable load discharged from each WWTP is determined, taking into account the type and the specific characteristics of the receiver, the category of its use, and the construction of the wastewater outlet.

The degree of wastewater treatment is determined to take into account the degree of wastewater mixing with the receiving water and its background quality (Ministry of Natural Resources 1991, 1999). The above approach is still used, among others in Russia, Moldova, Kazakhstan, Uzbekistan, and other countries of the former Soviet Union (Buijs 2007, 2009; OECD 2011). Increasingly due to the high pollution degree of the aquatic environment, the quality standards set for surface waters being the wastewater receivers are often related directly to wastewater introduced into the receivers, i.e., the degree of wastewater dilution with the receiver water is not taken into account in this case. An overview of the analyzed legal requirements from non-EU countries and regions for regulating the conditions of wastewater discharges is presented in Tables and .

Table 2

CountryWater categoryCOD, mg/lBOD, mg/lNH4+–N, mg/lNO2−–N, NO3−–N, mg/lTN, mg/lPO43−–P, mg/lTP, mg/lReferencesRussiaIndustrial fishing areasn/na3.0b (BOD20)0.390.02 (NO2−–N) 9.1 (NO3−–N)n/n2.0 (0.2 in eutrophic waters, 0.15 in mesotrophic waters, 0.05 in oligotrophic waters)n/nMinistry of Natural Resources (1991, 1999), Gogina (2010)Source of water supply153.0 (BOD20)n/nn/nn/nn/nn/nRecreation and water sports306.0 (BOD20)n/nn/nn/nn/nn/nOpen in a separate window

Table 3

Country/regionWWTP categoryCOD, mg/lBOD5, mg/lNH4+–N, NH3–N, mg/lNO2−–N, NO3−–N, mg/lTN, mg/lPO43−–P, mg/lTP, mg/lReferencesBelarus<500 PE12535n/nan/nn/nn/nn/nMinistry of Environment (2012)501–2000 PE1203020n/nn/nn/nn/n2001–10,000 PE1002515n/nn/nn/nn/n10,001–100,000 PE8020n/nn/n20n/n4.5>100,000 PE7015n/nn/n15n/n2Switzerland200–10,000 PE60202 (sum of NH3–N and NH4–N)0.3 (NO2−–N)n/n0.8n/nThe Swiss Federal Council (1998)>10,000 PE45152 (sum of NH3–N and NH4–N)0.3 (NO2−–N)n/n0.8n/nChina (Taihu Lake catchment)n/n50n/n8 (NH4+–N, 5 in winter season)n/n15n/n0.5Li et al. (2012)USAn/nn/n30n/nn/n3–5 (areas sensitive to eutrophication)n/n1.0–0.1 (areas sensitive to eutrophication)Sedlak (1991), US EPA (2012)BC, CanadaStreams, rivers and estuariesn/n45 (10 if dilution ratio < 40:1)n/nn/nn/n0.5 (MDFb > 50 m3/d)1.0 (MDF > 50 m3/d)British Columbia Office of Legislative Counsel Ministry of Attorney General (2005), US EPA (2012)Lakesn/n45n/nn/nn/n0.5 (MDF > 50 m3/d)1.0 (MDF > 50 m3/d)Open marine watern/n130 (MDF > 10 m3/d)n/nn/nn/nn/nn/nCoastal watersn/n45 (MDF > 10 m3/d)n/nn/nn/nn/nn/nDubaiHarbor area100502 (NH4+–N)40 (NO3−–N)10 (TKNc)2n/nGovernment of Dubai (2010, 2018)Open Sean/n305 (NH3–N)n/nn/n0.1n/nOpen in a separate window

Methodology for determining the permissible concentrations of pollutants in treated wastewater in Russia

The current wastewater standards regulations in Russia provide a set of standardized indicators and determine their permissible values in surface waters for the following parameters: BOD, COD, total suspended solids (TSS), NH4+–N, nitrites (NO2−–N), nitrates (NO3−–N), and orthophosphates (PO43−–P) (Stefanova et al. 2019). Surface water bodies located in the Russian part of the Baltic Sea basin have been included in the areas of industrial fisheries, for which the most stringent standards are applied (Nikolajew et al. 2008). Therefore, maximum concentrations of pollutants in treated wastewater are set at a maximum permissible level of pollutants in surface waters used as fishery areas.

The standards for surface water quality in Russia are established depending on the category of their use and they are the basis for establishing the legal rules of wastewater discharge into surface waters. According to this approach, the quality of wastewater discharged into the receiver should be determined in such a way that after introducing the parameters of the receiver’s water quality do not exceed the set limits presented in Table depending on the type of water use. Moreover, this approach allows in each specific case to adjust the quality of treated wastewater to the condition in the receiver and its self-purification capacity.

Since northwestern regions of Russia with extensive urban-industrial agglomerations are located in the Baltic Sea catchment area (Sankt Petersburg and Kaliningrad), the limits for WWTPs discharging their effluents to the Baltic Sea are set according to HELCOM recommendations.

Quality standards for treated wastewater in Belarus

The objectives and basic principles of standardization in the field of water protection in Belarus are contained in the Technical Code under the title: “The order of establishing the norms of permissible discharges of chemical substances and other pollutants in wastewater composition” (Ministry of Environment 2012). Permissible concentrations of pollutants are set for COD, BOD5, TSS, NH4+–N, TN, and TP content depending on PE, determined based on the unit BOD5 load.

The permissible content of other pollutants in wastewater discharged into water receivers and the required level of their reduction are determined taking into account the intensity of wastewater outflow, the concentration of pollutants in the receiver and its assimilation capacity following the guidelines enclosed in the Technical Code (Ministry of Natural Resources 1991, 1999; Gogina 2010).

Effluent quality standards in Switzerland

Water governance in Switzerland is divided into three levels: federal, cantonal, and municipal (Federal Ministry of Environment Nature Conservation and Nuclear Safety 2002). The main legal framework governing water resources in Switzerland is the Federal Water Protection Law (WPL) defined at the federal level. Based on the WPL the Waters Protection Ordinance (WPO) was adopted on October 28, 1998 by the Swiss Federal Council and is still in force (Bucheli et al. 2010).

Switzerland as a non-EU country has its national legal regulations concerning water and wastewater management which mainly corresponds with EU water policy (Eggen et al. 2014). Besides the Swiss efforts for maintaining the waters quality at the national level, Switzerland fulfills its international responsibilities by active participation in international commissions such as the International Commission for the Protection of the Rhine, the International Commission for the Protection of Lake Constance, the Commission for the Protection of the Waters of Lake Geneva, the International Commission for the Protection of Italian-Swiss Waters, and the Commission for the Protection of the Marine Environment of the North-East Atlantic (Lieberherr 2011).

The Swiss legal requirements concerning municipal wastewater discharge are developed for basic parameters such as BOD5, COD, and TSS concerning also three main nutrients: ammonium, nitrites, and orthophosphates. However, the requirements for ammonium content are applied when it is potentially detrimental to the water quality of the water body, and if the wastewater temperature is higher than 10 °C. Additional requirements concerning orthophosphates discharged into sensitive waters apply in the lakes catchments, on watercourses beyond the lakes, and for WWTPs above 10,000 PE, situated on watercourses in the catchment area of the Rhine downstream of lakes (The Swiss Federal Council 1998). Dissolved organic carbon is also limited for effluents above 2000 PE. According to the WPO, the discharge concentrations and the removal efficiency are considered together, in contrast to EU standards where both criteria can be interchangeable.

Switzerland has achieved great success in reducing phosphorus loads (Brunner et al. 2019). The phosphorus concentrations in Swiss lakes have steadily declined since the 1980s (Rodríguez-Murillo et al. 2015) and the current state of Swiss lakes can be generally described as good (Tu et al. 2019). Unfortunately, due to the soil enrichment in phosphorus compounds on agricultural lands of high livestock density within the lake catchment areas, a further water quality improvement cannot be guaranteed for all lakes (Bucheli et al. 2010; Ferré et al. 2019). To provide the highest possible protection of the lakes susceptible to eutrophication the effluent quality requirements should be stricter for each wastewater receiver. For example, for wastewater discharged into Lake Lugano, the TP allowable concentration is set at the level of 0.3 mg/l (OECD 2007). So in the terms of eutrophication, the Swiss effluent standards take into account the sensitivity of individual receivers to eutrophication, treating phosphorus as a key factor.

Quality standards for treated wastewater in China

One of the characteristic features of surface waters state in China is the wide variation of water pollution levels in different geographic regions of the country. In general, the level of surface water pollution is relatively low, but in the Pearl and Yangtze river basins, one of the highest levels of water pollution is observed (Guo 2007).

The reason for the poor state of the water environment is the intensive industrial activity and a high degree of urbanization in the region (Yue et al. 2018). The worst situation associated with water eutrophication is observed in Lake Taihu located about 100 km west of Shanghai in the Yangtze River delta, which for centuries has served as a natural retention reservoir for irrigation of rice fields, fishing, and shipping. In 2007, the waters of the lake were classified into the lowest quality category (category V+) (Li et al. 2012).

To prevent a deteriorating of this situation, in 2008 the Ministry of the Environment Protection of China has established the special limits for wastewater discharges into water receivers in ecologically sensitive areas. New standards for the 11 quality parameters for industrial wastewater in the Yangtze basin were also developed (Wang and Wang 2009).

In the same year, the most stringent local standards for municipal wastewater discharge were established for the Lake Taihu catchment area, which covered the following four parameters: COD, NH4+–N, TN, and TP (Liu et al. 2013).

The low permissible concentration of phosphorus in treated wastewater allows concluding that also in China the key role of phosphorus in the development of eutrophication processes in inland waters is noticed. The permissible TP concentration at 0.5 mg/l is even more stringent than the standards applicable in most European countries. However, this value is a regional standard and is applied only in a specific catchment. In contrast, in the rest of China’s water areas, the permissible concentration of TP is established at the level of 1.0 mg/l and TN at 15 mg/l (Li et al. 2012).

The Chinese guidelines also require the limiting of NH4+–N content to a maximum of 8.0 mg/l (5.0 mg/l in winter season), which is considered to be one of the most eutrophic forms of nitrogen compounds (Zhang et al. 2015). As indicated by the experience from WWTPs in China, actually the municipal wastewaters are characterized by an unfavorably low ratio of COD to nitrogen (C/N), which causes a problem with biological denitrification, so the removal of TN is a great challenge (Bodik et al. 2009).

The methodology of determining the conditions for wastewater discharge into receivers, taking into account their regional characteristics, seems to be justified in such large and geographically and climatically diversified territories like China. A similar regional approach to regulations regarding the quality of wastewater discharged into receivers is also applied in the countries of North America—USA and Canadian provinces.

Quality standards for treated wastewater in the United States of America

Legal regulations regarding the wastewater discharge into surface waters in the United States are determined based on the water state of the receiver and its sensitivity to eutrophication (Carey and Migliaccio 2009). The USA, like China, has a wide territory with a large diversity of geographic, climatic conditions and the degree of urbanization. Unlike in China, the permissible values obligatory for the entire USA area are set only for BOD5 and TSS: for both parameters, the maximum permissible content in wastewater amounts 30 mg/l with a reduction of at least 85%, while the COD value in the national scale is not standardized (Sedlak 1991).

The permissible concentrations regarding the nutrients content in wastewater are set only for water bodies sensitive to eutrophication, e.g., Lakes Tahoe and Occoquan, Great Lakes, Chesapeake Bay, the northern part of the Gulf of Mexico, and others. In the USA, the quality standards of wastewater discharged into waters susceptible to eutrophication have a regional character (Li et al. 2012).

The conditions for wastewater discharge into water bodies exposed to eutrophication in the USA can be considered as one of the most stringent. The achievement of permissible effluent TP concentration of 0.1 mg/l (Sedlak 1991) is possible only when using exceptionally capital-intensive technologies, which are characterized by increased energy consumption and greenhouse gases emission, large amounts of chemical reagents, and high costs of processing and utilization of an increased amount of sewage sludge.

National guidelines applicable in the USA to treated wastewater discharged into the receivers resistant to eutrophication are much less restrictive. On the other hand, the lack of requirements regarding TN concentration standards makes it possible to avoid the use of expensive technological systems for advanced nitrogen removal and justifies the use of basic systems of biological treatment with chemical precipitation only when necessary. This approach seems to be justified from economic and ecological points of view.

Quality standards for treated wastewater in British Columbia (BC), Canada

In BC province, the quality of wastewater discharged into the receiver depends on the maximum daily wastewater flow rate from the treatment plant and the type of the receiver. Three WWTP capacity categories have been established by BC legislation: below 10 m3/d, 10–50 m3/d, and above 50 m3/d. Three types of receivers were also determined: (1) streams, rivers, and estuaries, (2) lakes, and (3) marine waters. The standard values for BOD and TSS were established with consideration of the properties of the receiver. The ratio of water receiver flow intensity to treated wastewater flow intensity is also taken into account: it allows to consider the degree of wastewater dilution. The 40:1 ratio was assumed as the limit value, while under the ratio below 10:1 the wastewater discharge is prohibited (British Columbia Office of Legislative Counsel Ministry of Attorney General 2005).

For the areas particularly sensitive to eutrophication the regulations should be more restrictive. For example, regarding the treated wastewater discharges to the Okanagan and Christina Lakes or the Thompson, Cowichan, Nicola, and Cheakamus rivers, the maximum permissible TP concentration in discharged wastewater is only 0.25 mg/l (US EPA 2017).

The conditions for wastewater discharge into surface wasters in BC do not include the obligatory requirements for effluent nitrogen content. Such requirement is applied in the case of chosen water bodies (Sedlak 1991). For example, for municipal and industrial wastewater discharged into Okanagan Lake the maximum concentration of TN is 6.0 mg/l (British Columbia Office of Legislative Counsel Ministry of Attorney General 2005). A methodological approach to standardizing the quality of wastewater discharged to receivers in Canada can also be referred to the regional approach considering the individual characteristics of different receivers.

Emirate of Dubai

Wastewater management in Dubai is a matter of special importance due to the lack of freshwater resources. The task of wastewater management is not only marine water protection but also the production and accumulation of additional water resources for the needs of residents and irrigation. The rapid population growth in the United Arab Emirates (UAE) along with intensive consumption of drinking water has put heavy pressure on the limited national water resources. Recycled treated wastewater is a valuable source of potable water that can be used as an alternative to marine water desalination (Khan and Dghaim 2016). The authorities of UAE aware of the validity of water issue importance and its influence on national income level from tourism, reveled in September 2017 the UAE Water Security Strategy 2036. This document aims to ensure sustainable access to water in line with standards of the World Health Organization and the UAE’s vision of sustainability and prosperity (UAE’s Ministry of Energy & Industry 2017).

The Dubai Emirate Government implemented the Water Environment Regulation EN-5.0 (Government of Dubai 2018) which defined the quality limits of wastewater discharge. Dubai’s legislation on treated wastewater discharge established the effluent quality standards depending on the type of two main receivers: the Dubai Harbor area and the open waters of the Persian Gulf. The effluent standards for wastewater discharge to the Dubai Harbor concern the content of NH4+–N, BOD5, COD, nitrate nitrogen (NO3−–N), total Kjeldahl nitrogen, and PO43−–P, while discharges limits to the open waters of the Persian Gulf concern the content of NH3–N, BOD5, and PO43−–P (Government of Dubai 2010, 2018).

These standards have been established to minimize the negative impact on the harbor and the Persian Gulf water quality, the Gulf ecosystem, and the local fishing industry (Government of Dubai 2018). The standards take into account not only total but also mineral forms of nutrients, while for more polluted port waters they are less restrictive.