The Importance Of Maintaining Wastewater Quality

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In the typical wastewater treatment process, the goal of primary, secondary and tertiary effluent treatment is to reduce or remove organic matter, solids, nutrients, disease-causing organisms and other pollutants from the treated wastewater before it is discharged to a body of water. In addition to disinfectants, other chemicals are sometimes added during the treatment process to help settle out or strip out nutrients including phosphorus or nitrogen. Some examples of nutrient removal systems include coagulant addition for phosphorus removal and air stripping for ammonia removal.

To ensure efficient operation of any wastewater treatment plant, three different but equally important sets of measurements must be analyzed.

  1. Parameters essential to cleaning processes: pH as measured at the inlet and dissolved oxygen (DO) as measured in the aeration tank
  2. Parameters essential to measuring efficiency: biological oxygen demand (BOD) and chemical oxygen demand (COD) as measured at the inlet and in the treated effluent
  3. Parameters essential to plant optimization: DO, ammonium, nitrate, nitrite and phosphorous
Chlorination/Dechlorination
During the multistage wastewater treatment process, disinfectants are added to treat disease-causing bacteria. Common disinfectants include chlorine gas and sodium hypochlorite (bulk and on-site generated). Residual levels of chlorine must be monitored and adjusted prior to discharge to avoid harming the environment.

In a typical sanitary wastewater treatment plant, chlorine is added to the effluent from the final clarifier as it enters the chlorine contact chamber. Excess chlorine is then removed in a dechlorination stage by adding sulfur dioxide, sodium bisulfite, sodium sulfite or sodium metabisulfite. During both the chlorination and dechlorination stages, chlorine concentration measurements are required and are typically achieved through the use of on-line continuous analyzers.

Ammonia, Nitrogen and Phosphorus
Monitoring ammonia levels in wastewater treatment and effluent discharges helps to ensure that the nutrient levels are sufficient to allow bacteria to break down waste in the treatment process while minimizing concentrations of ammonia in the final outfall so that the effluent is safe for wildlife. Additionally, ammonia monitoring is used to document discharge levels set by regulatory authorities, especially where non-compliance can result in penalties.

For control of a nitrification/denitrification process in a wastewater treatment plant, ammonia measurement is a must. Nitrate is a nutrient that will encourage undesirable, oxygen-depleting growth in rivers and lakes and is poisonous for fish and microorganisms. Phosphate in wastewater will also encourage growth in rivers and lakes. This eutrophication process causes algae and seaweed to amass, greatly impacting the ecological balance of the ecosystems.

Wastewater Quality Analyzers
As industries and municipalities are required to more stringently monitor wastewater parameters, demand grows for high-quality analytical instruments that facilitate regulatory compliance. Continuous, online instruments have gained popularity because they reveal more through their ongoing analysis and better identify contaminant sources and necessary process changes. Continuous instruments also operate and calibrate automatically, reducing the need for human intervention.

In addition, optimizing and controlling a wastewater treatment process is dependent on the availability of water quality data. Results from outside laboratory testing cannot be obtained as quickly as results from onsite water quality analytical instrumentation. Therefore, with properly maintained continuous online instruments, a wastewater treatment facility, whether municipal or industrial, can benefit from immediate data that can then be used to optimize their wastewater treatment process.

Advances in online instrumentation, covering the range of parameters critical to the optimization of the wastewater treatment process, have enabled the equipment to satisfy a range of budgets and technical requirements. For example, the Aztec Series 5000 Dissolved Oxygen (and Mixed Liquor Suspended Solids (MLSS) monitoring instruments offer the ability to simultaneously measure the oxygen content and the concentration of solids or biomass in a system. The system can be set up to measure DO or M.L.S.S. individually if so required. The instrument control system also can accommodate two measuring points, reducing costs for the operator. The Series 5000 is the only system that performs full self cleaning and calibration in situ without the need for an operator.

For the other critical parameters, Severn Trent Services offers the Aztec Series 1000 colorimetric or ion selective water/wastewater quality analyzers and MicroChem®2 transmitter, analyzer and controller to measure critical parameters including; aluminum, ammonia, bromine, chlorine dioxide, chlorine (free and total, buffered and bufferless), color, disolved oxygen, fluoride, iodine, iron, nitrate, nitrite, manganese, pH, phosphate, ORP, and silica.

SOURCE: Severn Trent Services