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How Effluent Compares to Storm Runoff in Relation with Surface Water Quality

By Nicholas Krebs



Waste water treatment plants are considered simple solutions for poor surface water quality and are used in every developed and developing society. There are varying types of waste treatment plants. The systems are rarely able to purify all water that passes through the system. The problem with a mix-and-treat waste water system is the strain from sudden influxes of water. Systems that combine storm runoff accept variability in the volume of water that needs treating. Effluent is discharged when the plant cannot treat all the waste. The purpose of this review is to determine which system is the closest to meeting the theoretical goal by analyzing the long-term effects of how effluent, verses unfiltered storm runoff, affect the quality of surface water. The results of this review will provide a direction for future research in determining a water treatment system with the least impact on the environment.

Key Terms:  Surface water quality, effluent, riparian buffer, Combined sewer system, storm runoff


The purpose of every water treatment plant is to convert non-potable water into water that is safe to ingest. Although there are a variety of systems designed for purpose of water purity, all water has undergone some process to ensure its quality for consumption. All water treatment centers used to treat public water utilize biological and chemical processes to purify water either for consumption or releasing it into a water body. The most common systems include a multi-step processes for removing unwanted particles from the water. The wastewater is sent through a screen to remove large physical objects from the water. The next stage is the grit chamber, where a difference in current speeds allows finer particles to settle to the bottom of the tank as waste while the water continues to a sludge tank. The sludge tank is used to breakdown organic particles in the water by hosting bacteria in the sludge and aerating the water. The water moves through a series of chambers. The first chamber is anaerobic, followed by anoxic and oxic tanks. Each one of the tanks targets a specific type of bacteria to exterminate from the water. The final two steps are to have the water move through various fine filters including a biofilm and then it is sent through a chamber where the water passes under a strong UV lamp to eliminate any other bacterium in the water1.

 Some water systems have storm runoff channeled through the water facility, Combined Sewer System, CSS.  The flaw in this type of system is that when the system is under too much strain it can result in combined sewer overflows, CSO. A CSO results in partially treated or untreated water being discharged as effluent into a water body2. In contrast, other city designs channel storm runoff directly into the surface water supply, collecting contaminants along the way3. In either system, contaminants are discharged into local ecosystems4-5. In this review, I will discuss the impact of these water systems on surface water quality and the surrounding ecosystem.


Combined Sewer systems are a common water infrastructure design. It consists of a treatment facility that has both sewage and storm runoff channeled into the plant. One benefit of a CSS facility is the dilution of pharmaceutical waste. The current water system techniques and filters are only capable of eliminating some pharmaceutical wastes from the water. Although the same amount of medical waste would be present in either system, because of the higher volume of water in a CSS the concentration is lower6. Water treatment facilities that treat storm runoff as well as waste water, results in the sporadic discharge of effluent. Effluent is water evacuated from the plant that has not been fully treated, still containing contaminants7. Combined sewer systems handle a higher volume of water than non-combined systems. The higher volume of water can decrease the concentration of pollutants bringing them within legal limits for potable water8.


Effluent is discharged because the water treatment plant receives a volume of water greater than the capacity for treatment at the site. Water discharges occur from combined sewer overflows2. The plants will evacuate some of the waters either treated, partially treated, or untreated. Partially treated water is when only a few preliminary steps of water treatment occur prior to discharge5. The minimum treatment water can receive and be considered partially treated is the initial passing though the screen and the final step of UV radiation1.  UV radiation is a crucial step in the process in order to prevent bacterium, including antibiotic-resistant bacteria, from replicating after the water is discharged9.


Long term effects of effluent in natural water systems has been the center for several studies. Often an overlooked aspect of CSO is the downstream effect. Multiple water treatment plants will need to discharge in a similar timeframe causing greater concentrations of E. Coli downstream2. Regular discharge of effluents into water bodies will result in elevated levels of nitrogen and phosphorus in the water10. Higher levels of nitrogen and phosphorus can drastically change ecosystems through eutrophication. The excess of nitrogen and phosphorus will alter populations within the ecosystem, most commonly increasing algae populations, decreasing the amount of dissolved oxygen in the system10. In some cases, the level of available oxygen can decrease to zero and forming dead-zones. Along the coast of the Gulf of Mexico there is a large dead-zone where the dissolved oxygen levels have been depleted to the point where only a select few organisms can survive in the area. The zone stretches from the Mississippi delta to eastern Texas.11


Storm runoff can provide varying strain on water treatment facilities. Storm water presents an unknown volume of water and contamination to some water infrastructure designs. The systems that treat storm runoff separately from sewage can avoid discharges of sewage effluent. The concentration of pollution from storm runoff varies with the physical components of the area12. There are methods for decreasing storm water pollutants without the use of a combined water treatment plant. In most cases runoff quality is managed through the upkeep of riparian buffers. In most cases these buffers are preferred for preventing sediments, nitrogen, and phosphorus from entering the water system13. The pollutants found in untreated storm runoff can be classified by PSD (Particle size distribution) and TSS (total suspend solids)12 ( Table 1.).

The effectiveness of riparian buffers was tested along the edge of the Jobos Bay watershed in Puerto Rico14. The study ran for three years and faced two tropical storms. The study was focused on three aspects of water flow impacted by riparian buffers. The study compared four zones of land two protected from the buffer one closest to buffer and one directly behind it and two unaffected land areas of approximately the same size. The results from the experiment determined that the areas impacted by the buffer showed an overall decrease in water by 16% and subsurface flow decreased by 99%, and the overall sedimentation had a decrease in 24% relative to the land-zones without a riparian buffer. The buffer demonstrated a decrease of Nitrogen by 31% and Phosphorus 29% in the water collected by the sampling wells14. Riparian buffers are also useful to combat temperature pollution of water systems. When the rain water hits the surface, the thermal energy leaves the surface and is transferred to the water. Due to waters high specific heat capacity, it is capable of carrying the thermal energy for long periods of time and will continually gain thermal energy as it travels across surfaces heated by the sun or other means. Riparian buffers aid in temperature control by slowing the rate of influx into the system, allowing the thermal energy time to dissipate. Buffers are also responsible for lower surface temperatures by shading the system from the sun as well as limiting the influence of wind on changing the systems temperature15.


 This research is important to everyday life because safe water is required in any functioning society. As water systems change with time to suite a growing population it is important to consider how the facilities will impact the environment. Future research in this area should consider different biological process for limiting the impact of effluent and surface runoff and how pharmaceutical waste in water should be treated3. Surface water quality is essential to a healthy community and a trademark of developed nations.4 When surface water quality is increased and preserved, all ecosystems will show an increased health and productivity.

Table 1. The average Total Suspended Solids (TSS) in Storm runoff, and Effluent around industrialized cities.

Type of Water TSS (PPM) Study
Storm runoff 150 Surface water quality in a water run-off canal system: A case study in Jubail Industrial City, Kingdom of Saudi Arabia16
Effluent 450 Developing the remote sensing-based early warning system for monitoring TSS concentrations in Lake Mead17

PPM = Parts Per Million


(1) Ben, W.; Zhu, B.; Yuan, X.; Zhang, Y.; Yang, M.; Qiang, Z. Transformation and fate of natural estrogens and their conjugates in wastewater treatment plants: Influence of operational parameters and removal pathways. Water Research 2017, 124 (Supplement C), 244-250, DOI:

(2) Jalliffier-Verne, I.; Heniche, M.; Madoux-Humery, A.-S.; Galarneau, M.; Servais, P.; Prévost, M.; Dorner, S. Cumulative effects of fecal contamination from combined sewer overflows: Management for source water protection. Journal of Environmental Management 2016, 174, 62-70, DOI:

(3) Huang, T.; Li, X.; Rijnaarts, H.; Grotenhuis, T.; Ma, W.; Sun, X.; Xu, J. Effects of storm runoff on the thermal regime and water quality of a deep, stratified reservoir in a temperate monsoon zone, in Northwest China. Science of The Total Environment 2014, 485, 820-827, DOI:

(4) Paule-Mercado, M. A.; Lee, B. Y.; Memon, S. A.; Umer, S. R.; Salim, I.; Lee, C. H. Influence of land development on stormwater runoff from a mixed land use and land cover catchment. Science of The Total Environment 2017, 599, 2142-2155, DOI:

(5) Odjadjare, E. E. O.; Obi, L. C.; Okoh, A. I. Municipal Wastewater Effluents as a Source of Listerial Pathogens in the Aquatic Milieu of the Eastern Cape Province of South Africa: A Concern of Public Health Importance. International Journal of Environmental Research and Public Health 2010, 7 (5), 2376-94.

(6) Yang, Y.; Ok, Y. S.; Kim, K.-H.; Kwon, E. E.; Tsang, Y. F. Occurrences and removal of pharmaceuticals and personal care products (PPCPs) in drinking water and water/sewage treatment plants: A review. Science of The Total Environment 2017, 596-597 (Supplement C), 303-320, DOI:

(7) Madoux-Humery, A.-S.; Dorner, S.; Sauvé, S.; Aboulfadl, K.; Galarneau, M.; Servais, P.; Prévost, M. The effects of combined sewer overflow events on riverine sources of drinking water. Water Research 2016, 92, 218-227, DOI:


(9) Guo, C.; Wang, K.; Hou, S.; Wan, L.; Lv, J.; Zhang, Y.; Qu, X.; Chen, S.; Xu, J. H2O2 and/or TiO2 photocatalysis under UV irradiation for the removal of antibiotic resistant bacteria and their antibiotic resistance genes. Journal of Hazardous Materials 2017, 323, Part B, 710-718, DOI:

(10) Ghazouani, M.; Akrout, H.; Jomaa, S.; Jellali, S.; Bousselmi, L. Enhancing removal of nitrates from highly concentrated synthetic wastewaters using bipolar Si/BDD cell: Optimization and mechanism study. Journal of Electroanalytical Chemistry 2016, 783 (Supplement C), 28-40, DOI:

(11) Ulloa, M. J.; Álvarez-Torres, P.; Horak-Romo, K. P.; Ortega-Izaguirre, R. Harmful algal blooms and eutrophication along the mexican coast of the Gulf of Mexico large marine ecosystem. Environmental Development 2017, 22 (Supplement C), 120-128, DOI:

(12) Charters, F. J.; Cochrane, T. A.; O’Sullivan, A. D. Particle size distribution variance in untreated urban runoff and its implication on treatment selection. Water Research 2015, 85, 337-345, DOI:

(13) Thomas, P.; Rahman, M. S. Region-wide impairment of Atlantic croaker testicular development and sperm production in the northern Gulf of Mexico hypoxic dead zone. Marine Environmental Research 2010, 69 (Supplement 1), S59-S62, DOI:

(14) Williams, C. O.; Lowrance, R.; Bosch, D. D.; Williams, J. R.; Benham, E.; Dieppa, A.; Hubbard, R.; Mas, E.; Potter, T.; Sotomayor, D.; Steglich, E. M.; Strickland, T.; Williams, R. G. Hydrology and water quality of a field and riparian buffer adjacent to a mangrove wetland in Jobos Bay watershed, Puerto Rico. Ecological Engineering 2013, 56 (Supplement C), 60-68, DOI:

(15) Dugdale, S. J.; Malcolm, I. A.; Kantola, K.; Hannah, D. M. Stream temperature under contrasting riparian forest cover: Understanding thermal dynamics and heat exchange processes. Science of The Total Environment 2018, 610-611 (Supplement C), 1375-1389, DOI:

(16) Imen, S.; Chang, N.-B.; Yang, Y. J. Developing the remote sensing-based early warning system for monitoring TSS concentrations in Lake Mead. Journal of Environmental Management 2015, 160 (Supplement C), 73-89, DOI:

(17) Siddiqi, Z. M.; Saleem, M.; Basheer, C. Surface water quality in a water run-off canal system: A case study in Jubail Industrial City, Kingdom of Saudi Arabia. Heliyon 2016, 2 (6), e00128, DOI:


Cite this article:

Krebs, Nicholas. “How Effluent Compares to Storm Runoff in Relation with Surface Water Quality.” The D.U.Quark, 2, 2 (2018): 16-21.

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