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The Clean Water Act and wastewater discharge
Wastewater discharged to surface water without a proper control can pollute rivers and lakes, and even ground water. To protect water in the US from pollution by discharged wastewater, the Clean Water Act (CWA) was established in 1972 as amendments to and replacement of the Federal Water Pollution Control Act of 1948.
In Europe, water pollution is regulated under the Water Framework Directive , which lays down a strategy against water pollution and requires all the member states to participate. The Directive involves the identification and monitoring of priority hazardous substances that threaten human health.
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NPDES permits for wastewater discharge
National Pollutant Discharge Elimination System (NPDES) permit program, created in CWA, is used to regulate direct wastewater discharge of pollutants into water in the US from point sources. The EPA authorizes the state, tribal, and territorial governments for granting the NPDES permits and enforcement of the monitoring. The wastewater sources that are required for NPDES permits include municipal wastewater, industrial wastewater, animal feeding operation wastewater, agricultural wastewater and storm waters that discharged from different sources and activities.
Different municipal facilities require different NPDES permits depending on the requirement of the receiving water. Direct discharge of more than 50 categories of industrial wastewater also require different NPDES permits; effluent guidelines are used to determine the amount of pollutants allowed for direct discharge of different categories of industrial wastewater in the NPDES permits. If the industrial wastewater is discharged to a municipal wastewater sewer system (indirect discharge), no NPDES is needed but local municipal permits may be required and pretreatment of the wastewater may be necessary. If industrial wastewater is indirectly discharged, the receiving municipal facility needs to monitor the industrial wastewater flowing into wastewater facility, test the final effluent from the mix of residential sewage wastewater and the industrial wastewater, and compile the test results in the laboratory information management system (LIMS) and report to regulatory authorities.
Wastewater and surface water testing
Wastewater testing varies depending on the different NPDES permits. For municipal wastewater tests, four different categories of testing are often required: physical properties, solids, biologicals, and chemicals. For industrial wastewater, different heavy metals may also be required to be monitored.
Surface water, the receiving water for discharged wastewater, is also monitored to make sure that it does not contain contaminants higher than the standards. For instance, high concentration of nutrients (total nitrogen and total phosphorus) in surface water contribute eutrophication, which depletes oxygen in water, leading to algal bloom (production of mycrocystins), bacteria growth, and death of aquatic animals.
The table below lists some of the wastewater tests that are often necessary to conduct in a certified laboratory using different analysis tools. Some of these tests are for the facility operation, such as common anions testing.
|Alkalinity||Total dissolved solids||Bioassays (bioactivity of a substance on cells)||Biochemical Oxygen Demand (BOD)||Ammonia||Chlorine residual after disinfection to kill microbial pathogens|
|Conductivity||Total fixed solids||Toxicology assays for mortality and maybe reproduction testing using animals, such as fish||Chemical Oxygen Demand (COD)||Nitrite, nitrite, Total Kjeldahl nitrogen, total nitrogen||Metals (Ba, Ca, Cd, Cr, Cu,Fe, K, Mn, Mg, Na, Ni, p, Pb, Zn)|
|pH||Total solids||Microbiology tests for coliforms and other pathogens after disinfection||Disolved Oxygen (DO)||Total phosphorus||Common anions including sulfate|
|Turbidity||Total suspended solids||Oil and grease||Organic contaminants (PCBs and semi-volatiles)|
|Color and odor||Total volatile solids||Total organic carbon|
The testing results will also be a good indicator or reference for wastewater treatment steps (primary, secondary, and maybe tertiary as well) to ensure the final treated wastewater effluent meets permit requirements before discharge into the receiving surface water.
Physical property of wastewater testing includes measuring temperature, pH, conductivity (salinity) and turbidity. Color and odor are characterized as well. For instance, a too high or too low pH in wastewater can affect the aquatic lives in receiving water as they only live in neutral or slightly basic water environment.
Solids include dissolved, suspended, and settled solids. Total suspended solids (TSS), for instance, allows water to absorb more light, and therefore increases water temperature and reduces dissolved oxygen. This eventually negatively impacts or even kills aquatic animals. Total dissolved solids (TDS) on the other hand contain high concentrations of salts (chloride, sulfate, calcium and magnesium), and receiving water containing high TDS is not suitable for irrigation and industrial reuse.
Biological measurements include bioassays and coliform measurements. Bioassays help understand wastewater contaminants’ harmful effects on living organisms (plants and animals) or cells. Coliform index gives indicators on the presence of possible intestine pathogens.
Aquatic animals require dissolved oxygen (DO) in water to live. Aerobic bacteria can degrade organic matters using dissolved oxygen in water and BOD measures the amount of oxygen used up by bacteria for degrading organic matter. BOD is an indicator for the amount of organic materials in the wastewater effluent. If an effluent wastewater sample has a high BOD measurement , the bacteria in the wastewater will digest the organic materials from the wastewater and use up the oxygen in the receiving surface water, negatively affecting the aquatic lives. The goal of the wastewater treatment is to reduce the BOD value in wastewater.
COD is a measure of total oxygen used to break down both biologically-used organic matter (indicated by BOD) and inert organic matter. Because BOD measures oxygen in a biological process that may take 5 days, it is a much slower measuring process compared to COD, which can only take a few hours.
Wastewater from agriculture, animal feeding, storm water runoff and municipal facilities may all contribute to the blame of algal blooming due to excess amount of nutrients in surface water. The overgrowth of algae using excess amounts of nitrogen (from ammonia, nitrite, nitrate and organic nitrogen) and phosphorus in surface water causes production of neutoxins (microcystins) that may contaminate future drinking water and threaten human health. The algae further eaten up by bacteria use up the dissolved oxygen in surface water and lead to death of aquatic animals. To protect the public health, a nitrogen and phosphate test requirement has been added to some of the NPDES permits and a variety of methods can be used for nutrient analysis.
The colorimetric analysis and automated photometric assays are fast and cost-effective for total nitrogen and total phosphate tests. In addition, the recently developed ion chromatography method to analyze total nitrogen and total phosphorus in a single chromatography run after a single digestion is also effective.
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The major source of heavy metal contamination is industrial wastewater from textile, paper and pulping, semi-conductor, metal finishing and plating, and many other industrial categories. Besides the notorious top 4 heavy metals , other metals, such as chromium, nickel, and zinc (see table above) are also toxic to human health.
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Organic contaminants and emerging contaminants
Emerging contaminants, such as pharmaceutical and personal care products (PPCPs), hormones, and endocrine disrupters, have recently caused public health concerns. Many of them are still in the study stage and their exact health effects are still not clear. Although they are not currently regulated by government authorities, many analytical methods to analyze emerging contaminants with targeted and untargeted approaches are under development. High resolution mass spectrometry (HRMS) coupled with liquid or gas chromatography is a powerful tool for determination of this dangerous class of contaminants.