Sampling is a critical step in Wastewater Monitoring. How can practitioners ensure the collection of representative samples? This article provides a brief overview of the key considerations.
To guarantee the representativeness of collected samples, practitioners must accurately verify the total wastewater discharge volume. During sampling, two types of collection points are typically utilized:
1.Sampling points are located at the discharge outlets of workshops, workshop treatment facilities, or specialized pollutant treatment facilities;
2.Sampling points are set at the external discharge outlets of pollution-generating units. Specifically, when conducting effective Online Water Quality Monitoringfor various wastewater treatment units, sampling points should be installed at the inlets and outlets of treatment facilities (e.g., at the entry points of wastewater into treatment units and the exit points of treated effluent from these units).
Beyond the above scenarios, practitioners may encounter unexpected events during monitoring. For instance, if wastewater from ground flushing or equipment maintenance is discharged into treatment facilities, such discharges can disrupt total volume accounting. High-concentration wastewater entering the facilities may lead to an overestimation of the enterprise’s actual total discharge, while low-concentration (diluted) wastewater may result in underestimation. In such cases, the collected samples lose representativeness and accuracy. Therefore, practitioners must master key information related to pollution source discharge, including process flows, discharge patterns, and municipal pipeline networks. Samples should be collected during stable discharge periods, with real-time monitoring to record abnormal concentration-volume events and their occurrence cycles for subsequent analysis.
Key Considerations for Total Wastewater Volume Accounting During Sampling
When conducting acceptance inspections of enterprise wastewater discharge, the following points require attention:
1.For enterprises subject to total wastewater discharge assessment, the total volume can be calculated as the product of the daily average concentration and discharge volume. For enterprises without installed wastewater flow meters, recent water consumption invoices (e.g., from the past few months) should be requested for verification;
2.Fractional water quality treatment can be applied to samples. If production and domestic wastewater containing the same pollutant cannot be clearly distinguished, the enterprise’s water consumption data and water balance diagrams from environmental impact assessment (EIA) documents should be used to calculate the discharge volume of different wastewater streams;
3.For enterprises with significant monthly fluctuations in water consumption and discharge, water usage and discharge should be verified separately across peak, normal, and low-demand periods. Under the premise of accurate water quality monitoring, scientific analysis of pollutant indicators in wastewater should be conducted.
