2.4.3.Discharge standard setting

Categories: 2.4 Discharge Standards
Time of issue: 2022-05-16 11:15:48
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The setting of rural wastewater discharge standards is related to a series of issues such as process selection, equipment configuration, and operation and maintenance costs of treatment facilities. Low discharge standards will not help improve the rural living environment, and high discharge standards will lack practical feasibility, resulting in the inability to operate stably for a long time. The Chinese government attaches great importance to discharge standard setting for rural wastewater treatment. In 2018 and 2019, the competent authorities issued normative documents respectively to promote the formulation of local discharge standards in various regions; the corresponding work has also been completed basically in most provinces.

In the "Guidelines for the Compilation of Water Pollutant Discharge Control Specifications for Rural Domestic Wastewater Treatment Facilities (Trial)" issued in 2019, the competent government departments have targeted the selection and limit values of control indicators, emphasizing that measures should be taken according to local conditions and technical feasibility. Relying on the technical level and economic conditions, the pollution control level that can be achieved by related technologies should be considered fully, and the economic affordability and management level of rural areas should be taken into account.

The basic control indicators are pH, chemical oxygen demand (CODCr) and suspended solids (SS), and the optional control indicators mainly involve nitrogen and phosphorus. "Discharge Standard of Pollutants for Urban Sewage Treatment Plants"(GB 18918-2002) includes 12 basic control indicators (pH, CODCr, SS, NH3-N, TN and TP, etc., shown in Table 4.2 for details). In contrast, the selection of water pollutant discharge indicators for rural wastewater treatment facilities has been significantly reduced, taking into account the treatment costs and the accessibility of actual effects.

The scale of rural wastewater facilities is generally limited to less than 500m3/d, and the index limit refers to the Pollutant Discharge Standard for Urban Sewage Treatment Plants (GB 18918-2002), and is formulated according to the requirements of receiving water bodies. When the receiving water bodies belong to GB 3838-2002 surface water Class II and III functional water areas, the discharge standard refers to the first B level standard for urban sewage discharge; When the receiving water bodies belong to GB 3838-2002 surface water class IV and V functional water areas, the discharge standard refers to the second level standard; When the receiving water bodies belong to those with unclear environmental functions such as ponds near villages, the discharge standard refers to the third-level standard.

However, the discharge standards formulated by various provinces are stricter generally. Taking Shanxi Province as an example. In the "Pollutant Discharge Standard for Rural Wastewater Treatment Facilities in Shanxi Province" DB14/726-2019 issued in November 2019, ammonia nitrogen was added to the basic control indicators. When the receiving water bodies belong to GB 3838-2002 surface water Class II and III, the COD_Cr and NH₃-N refer to the first A level of the urban sewage discharge standard. Correspondingly, when the receiving water bodies belong to GB 3838-2002 surface water Class IV and V, the discharge standards of rural wastewater refer to the first A level and the first B level of the urban sewage discharge standard, seen in Table 2.4.

Table 2.4 Discharge Standards Comparison between Urban Sewage Treatment Plants and Rural Wastewater Treatment in Shanxi

Indicators	Discharge Standard of Pollutants for Urban Sewage Treatment Plants GB 18918-2002				Pollutant Discharge Standard for Rural Wastewater Treatment Facilities in Shanxi DB14/726-2019
	First Level		Second Level	Third Level	First Level	Second Level	Third Level
	First A	First B	Second Level	Third Level	First Level	Second Level	Third Level
	Basic control indicators				Basic control indicators
pH	6-9				6-9
COD	50	60	100	120	50	60	80
SS	10	20	30	50	20	30	50
ammonia-nitrogen	5(8)	8(15)	25(30)	/	5(8)	8(15)	15(20)
	Basic control indicators				Optional control indicators
total nitrogen	15	20	/	/	20	30	/
total phosphorus	0.5	1	3	5	1.5	3	/
animal and vegetable oil	1	3	5	20	3	5	10
petroleum	1	3	5	15
anionic surfactant	0.5	1	2	5
chroma	30	30	40	50
biochemical oxygen demand	10	20	30	60
number of fecal coliforms	10³	10⁴	10⁴	/

Note: The value outside the brackets is the control index when the water temperature is >12℃, and the value in the bracket is the control index when the water temperature is ≤12℃.

It shows that, although the competent authorities emphasize constantly on adapting measures to local conditions, taking into account the technical accessibility and the economic affordability and management level of rural areas, the discharge standards issued by various provinces still approach to higher standards and stricter requirements. Among them, stricter discharge standards for nitrogen and phosphorus mean that it is necessary to increase and strengthen the denitrification and phosphorus removal process in rural wastewater treatment, which will increase investment costs and operation and maintenance costs. Considering the practical problems of small scale and high impact load faced by rural wastewater treatment, it will increase the operation and maintenance cost sharply, which is unbearable in many areas and may lead to an unsustainable development situation.