Water Reuse

Common Contaminants in Wastewater

Due to the fact that wastewater is generated by a variety of sources (bathing, cooking, manufacturing, cleaning, etc.), the contaminants found in wastewater are varied and numerous.  They include, but are not limited to, organic material, pathogens, metals, salt, ammonia, pesticides, pharmaceuticals, and endocrine disruptors.  Some, such as pathogens and heavy metals, are undesirable in all treatment plant effluents as they are harmful to both humans and the environment.  Others, such as nitrates and phosphorus, can be deleterious if the effluent is being discharged to receiving waters but advantageous if the effluent is going to be reused for agricultural irrigation.  Therefore, it is important to understand that different uses of wastewater effluent will require different levels of contaminant elimination.

Most conventional wastewater treatment plants discharge into streams, lakes, and rivers (receiving waters).  These plants must have a NPDES (National Pollutant Discharge Elimination System) permit that determines the type and amount of contaminants they can discharge into the receiving water.  Most NPDES permits regulate BOD, TSS, pH, coliforms, and nutrients although the acceptable levels will vary depending on the wastewater treatment process and the use and health of the receiving waters.

Contaminants, such as metals, TDS, pharmaceuticals, and endocrine disruptors, may or may not included in NPDES permits; however, they can be detrimental to water reuse.  Some of these contaminants are just now being studied and their effects on the environment, humans, and reuse are unknown.

Biochemical Oxygen Demand (BOD)

BOD is a measure of how much organic material is in the wastewater plant effluent calculated by the amount of oxygen used by microorganisms in the oxidation of organic matter.  If the amount released in the effluent is too high, microorganisms in the receiving waters will eat the organic material utilizing dissolved oxygen as they do so.  This depletes the dissolved oxygen available to aquatic life and results in fish kills, invasions of weeds, and changes in the body of water.

Total Suspended Solids (TSS)

Total suspended solids are organic and inorganic solid materials that are suspended in water.  High concentrations of suspended solids can lower water quality by absorbing light.  Waters then become warmer which lessens the ability of the water to hold oxygen necessary for aquatic life.  Because aquatic plants also receive less light, photosynthesis decreases and less oxygen is produced.  Suspended solids can also clog fish gills, reduce growth rates, decrease resistance to disease, and prevent egg and larval development.  The material that settles fills the spaces between rocks and makes these microhabitats unsuitable for various aquatic insects.

pH

pH is a measure of the acidity of the water.  Most organisms thrive in a fairly neutral environment, pH of 6 - 9, and will die or have reproductive problems if the pH is too high or too low.

Coliform bacteria

Coliform bacteria are found in abundance in raw wastewater but their numbers are reduced through the disinfection step of the treatment process.  These organisms do not normally cause disease but are used as indicator organisms for disease-causing organisms called pathogens.  If a wastewater plant's effluent contains large numbers of coliform bacteria, it is likely that a large number of pathogens are also being released into the environment.  These pathogens can present a major health hazard.

Nutrients

Nutrients especially nitrates and phosphorus, can also cause problems in receiving waters.  Large amounts of these nutrients will lead to extensive growth of aquatic plants, algae, and plankton.  This process is called eutrophication.  It disturbs the eco-system and damages the biodiversity and flora.  As a result, the plants use up more oxygen when they decompose, and this leads to oxygen depletion in the water resulting in the death of fish and other aquatic creatures.  Phosphorus in wastewater comes from food, pesticides, and industries.  Nitrates in wastewater come from ammonia being converted to nitrates by bacteria in the treatment process.

Metals

Metals are present in wastewater mainly due to manufacturing processes, industries, and piping in household plumbing and collection systems.  Heavy metals found in wastewater include lead, silver, mercury, copper, nickel, chromium, zinc, cadmium, and tin.  These metals, when found in sufficient concentrations, can be detrimental to human health as well as the environment.  If wastewater is used to irrigate fields without having the metals removed, they will accumulate in the soil and may infiltrate the groundwater or render the fields useless.

Total Dissolved Solids

Total dissolved solids comprise inorganic salts (principally calcium, magnesium, potassium, sodium, bicarbonates, chlorides and sulfates) found in wastewater.  Effluent with high levels of TDS are not suitable for irrigation or landscaping because many plants are intolerant of the chlorides and the TDSs may leach into the groundwater.  TDSs are also not desirable for industry reuse because they will cause corrosion and incrustation.

Pesticides/Endocrine Disruptors

An endocrine disruptor is a synthetic chemical that when absorbed into the body either mimics or blocks hormones and disrupts the body's normal functions. This disruption can happen through altering normal hormone levels, halting or stimulating the production of hormones, or changing the way hormones travel through the body, thus affecting the functions that these hormones control. Chemicals that are known human endocrine disruptors include diethylstilbesterol (the drug DES), dioxin, PCBs, DDT, and some other pesticides.

These chemicals are present in wastewater due to pesticide use and application, manufacturing, and industries.  While human health effects of endocrine disruptors are still being investigated, numerous studies have shown that these chemicals have negative effects on the environment.  Releasing them into the environment or to humans through wastewater discharge and/or reuse may cause unknown problems now and into the future.

Pharmaceuticals

Since most medications are not wholly absorbed into the body, the excess is eliminated and enters the sewer system.  In addition, many people, hospitals, and nursing homes dispose of unused medications down the toilet.  These pharmaceuticals make their way to the wastewater treatment plant where little is done to remove them.  They are then released into the receiving waters dosing wildlife and even humans with drugs they don't have prescriptions for.  Studies are underway to determine the effects these medications are having but it is clear that eliminating them before reuse and/or discharge will be necessary in the near future.

 Sources:
http://www.ndhealth.gov/wq/sw/Z6_WQ_Standards/WQ_TSS.htm
http://www.nrdc.org/health/effects/qendoc.asp
http://www.co.el-dorado.ca.us/emd/envhealth/coliform.html
http://www.water-research.net/totaldissolvedsolids.htm
http://www.mtech.umd.edu/MTES/docs/PMG%20metal%20precip%20man-1.pdf