Methods and means of water quality control for natural and waste water

Regular monitoring of surface water sources

The water quality in surface water bodies used for household and agronomic needs requires constant monitoring. Studies are conducted at least once a month, with sampling points determined depending on the sanitary and hydrological conditions of the site. On rivers and canals, samples must be taken directly at the water intake point and 1 km upstream. On lakes and reservoirs, measurements are taken at a distance of 1 km from the water intake point at two diametrically opposite locations.

• Frequency of water body monitoring — at least once a month
• Monitoring of wastewater treatment — once every 10 days
• Deadline for starting analysis — no later than 12 hours
• BOD determination temperature — 20°C

In addition to laboratory analysis of samples, automatic monitoring stations capable of continuously recording 10 or more water parameters are actively used in practice. Domestic mobile complexes allow for the prompt tracking of critical indicators in field conditions. Such systems ensure a high level of accuracy and cover the entire working range of measurements.

Mobile stations record the concentration of dissolved oxygen (up to 0.025 kg/m³), electrical conductivity (from 10⁻⁴ to 10⁻² Ohm/cm), hydrogen index pH (from 4 to 10), temperature (from 0 to 40°C), water level (from 0 to 12 m), and the content of suspended solids (from 0 to 2 kg/m³). Specialized technical systems are used for stationary work and complex analysis.

Laboratory control and wastewater quality indicators

At treatment facilities for agricultural and industrial sites, the composition of source and treated water is assessed, and the efficiency of the treatment system itself is checked. According to regulations, this control is carried out once every 10 days. In laboratory conditions, organoleptic indicators, pH, the amount of suspended solids, chemical oxygen demand (COD), biochemical oxygen demand (BOD), dissolved oxygen, and harmful substances with regulated maximum permissible concentrations (MPC) are measured.

Of the organoleptic indicators, odor and color are checked. Chromaticity is determined by measuring the optical density of the sample on a spectrophotometer at different wavelengths. Acidity (pH) is calculated by an electrometric method: the potential of a glass electrode changes by a constant value at a given temperature (by 59.1 mV at 298° K or by 58.1 mV at 293° K). For this, KP-5, MT-58, LPU-01 brand pH meters and similar ones are used.

The COD value reflects the amount of oxygen required for the oxidation of all reducing agents by a solution of potassium dichromate in sulfuric acid. Analysis is carried out using arbitration methods (high accuracy during prolonged research) or accelerated methods for daily treatment monitoring with a stable composition of wastewater. The BOD indicator (most often five-day, BOD₅) records the oxygen consumption for the biological oxidation of organic matter in 1 l of water at 20°C under aerobic conditions.

The concentration of dissolved oxygen is measured before discharging treated wastewater into a water body to assess its corrosive properties and calculate BOD. For values greater than 0.0002 kg/m³, the iodometric Winkler method is used; for smaller values, colorimetric methods based on dye color change are used. For automatic measurements, EG-152-003 devices (range 0...0.1 kg/m³) or "Oksimetr" (ranges 0...0.01 and 0.01...0.02 kg/m³) are used. The concentration of regulated harmful substances is controlled at all stages of treatment.