Impacts of Waste-water on the Environment, Treatment Objectives and Disposal Regulations

There is no denying the fact that waste-water will have a lot of impacts on our environment, most of which may not be favorable to the plants, animals and man at all times. Sequel to this, there is a clarion call for the treatment of the said waste-water before disposal.

In order to achieve this, a well thought out treatment objectives have to be postulated and pursued vigorously. In order not to deviate or cause more problems with the treated waste-water, there is the need to develop and have functional disposal regulations that will guide men as they do this all important function.

Impact of Waste-water on the Environment

According to the Oxford Advanced Learners Dictionary of Current English, the word impact means among other things, the powerful effect that something has on somebody or some other thing(s)‘.

The question now is what are the powerful effects has waste-water on man‘s total environment? This will be viewed in two perspectives; negative impacts of waste-water, impact of waste-water disposal on the site.

Negative Impacts of Waste-water

There is no gainsaying the fact that waste-water has a lot of negative impact on the environment in which it is found. In order words, there are some noticeable effects of waste-water on and in wherever it is found.

In our previous units we saw the characterization of waste-water and found out that it contains sewage, which contains things like faeces, urine etc. and gray water which results from washing, bathing and meal preparations and then the storm water which results from surface run- off.

Agricultural run-off water and waste from nearby industries may also enter the system, etc. One or a combination of the above whenever present poses a threat to the nearby surrounding.

Apart from defacing the environment in which it is found, causing unsightliness to the people who may pass by, it is equally odorous as it emits obnoxious odour.

The waste-water wherever it is found occupies space that could have been used for another purpose impacting negatively on same. Also of importance is the fact that it is a breeding focus for mosquitoes and other insects including some helminthes.

Waste-water especially storm water impacts negatively erosion wise eroding the topsoil most of the time and destroying our possessions as it does so.

Of importance is the fact it also, with accumulated debris causes blockage of our drainage lines and enters into the compound of people destroying people’s property.

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Waste-water in rivers, streams, lakes or even oceans results to pollution. Scientific evidence supports significant impact of sewage pollution on water quality and health of sea grasses and corals (Lapoint, 2004).

Nutrient levels in sewage pollution are considerable relative to the low nutrient environment of the marine waters surrounding the islands.

Dissolved inorganic nitrogen (DIN) composed of ammonium (NH₄+ ), nitrate ( N0₃– ), and nitrite ( N0₂– ) is causing an excessive biomass of macroalgae that overgrow sea grasses and adult corals, obstruct development of juvenile coral, and develop areas of anoxia and hypoxia, depleting fish populations and other biological diversity (Lapointe, 2004).

Furthermore, sewage contamination in the marine ecosystem surrounding the Keys is a public health hazard due to known microbiological components such as Escherichia coli and Enterococcus.

Waste-water is richly blessed with disease pathogens and is ready to infect people and animals (both aquatic and terrestrial) around it. It is mostly because of this factor that there is the need to have it treated to some reasonable extent before reuse or disposal.

A look at the table below will show the pathogens most likely to be found in waste-water / water. The list in the table is never exhaustive of microbes that are pathogenic in the waste-water. It has no helminthes in them in the first place.

Impact of Waste-water Disposal on the Site

The impact of waste-water disposal on the site depends on the scope or nature of treatment given to the waste-water in question before the disposal. Rural areas have the highest numbers of septic systems because municipal infrastructure is not in place to convey sewage from homes and business to central sewer treatment plants.

The United States Environmental Protection Agency says adequately managed decentralized waste-water systems are a cost-effective and long-term option for meeting public health and water quality goals, particularly in less densely populated areas (USEPA, 1997).

Although current onsite sewage treatment methods are somewhat effective at reducing pathogens in waste-water, nutrient levels are not significantly decreased.

The implication is that whereas waste-water can be a source of pollution of the immediate environment, it can be of help to farmers who may need such nutrients.

Nutrient couplings between onsite waste-water systems and adjacent marine waters were studied by LaPointe et al. (1990) between December 1986 and September 1987.

Monitoring wells were installed on seven residential lots that were inhabited for at least 3 yr and up to 20 yr (LaPointe et al., 1990). The wells were installed in pairs, one near the septic system and the other midway between the septic systems and adjacent canals at each residential lot.

Water samples were collected monthly from every well and analyzed for salinity, temperature, and dissolved inorganic nutrients (Lapointe et al., 1990). Two statistical comparisons were made in this study.

First, monthly groundwater and surface water nutrient concentration data from the winter and summer were pooled separately to determine any significant difference between the wet and dry season (LaPointe et al., 1990).

Second, the pooled seasonal nutrient data from both monitor wells at the residential sites was compared to the control data. Nutrient enrichment was significant (up to 5000 fold) with the highest concentrations of ammonium, nitrate plus nitrate, and soluble reactive phosphate occurring in monitoring wells adjacent to septic system drain fields as compared to the control ground waters (Lapointe et al., 1990).

Lower concentration of these nutrients, although still enriched, occurred in ground waters extracted from wells installed midway between septic system drain fields and surface waters. Lowest concentrations of nutrients occurred in control ground waters extracted from wells installed within the Key Deer National Wildlife Refuge (Lapointe etal., 1990).

Mean concentrations of nutrients in ground waters decreased from winter to summer, contrasting with increases in measured nutrients in surface water from winter to summer.

Mean Values for Nutrient Concentrations (micromolar, μM)
Winter
Adjacent wells1	817	784	17
Midway wells1	118	256	2.54
Wells combined2	467	520	9.77
Control groundwater3	0.76	1.91	0.11
Canal4	1.61	0.88	0.15
Summer
Adjacent wells1	220	502	6.37
Midway wells1	30.7	188	1.62
Wells combined2	125	346	4.0
Control groundwater3	0.20	1.40	0.14
Canal4	3.22	1.69	0.43

Notes		Adjacent wells – water extracted from wells installed adjacent to septic systems, pooled data. Wells combined – water extracted from adjacent wells and midway wells, then pooled. Control groundwater – water extracted from monitoring well installed at Key Deer National Wildlife Refuge (KDNWR) Canal – Surface water collected from canal systems adjacent to septic system site Source: Adapted from Lapointe etal.,1990.

The elevated nutrient concentrations, summarized in the table above, indicate that waste-water effluent from septic systems is a significant source of enrichment to groundwater and surface waters in the Keys (Lapointe etal., 1990).

The predominant nitrogenous species in the groundwater was ammonium, likely caused by suboxic and anoxic conditions due to limited vadose zone underlying septic systems, preventing maximum nitrification (Lapointe et al., 1990).

The effects of treated waste-water especially sewage on the environment depends on the level of treatment and the population of the surrounding environment.

For instance, discharge of sewage into cesspits, shallow holes, and directly into the adjacent coastal water were common methods of sewage disposal during the years of early development of the Florida Keys. By then, ecological impact was minimal due to the sparse population common during the first half of the 20th century.

However, the Keys gradually became a popular vacation destination and a desirable place to live because of climate and proximity to pristine ocean waters. Since land area is limited, early subdivisions were high density with 50 foot by 50 foot lot sizes not uncommon (Kruczynski and McManus, 2002).

Direct release of untreated sewage resulted in nutrient enrichment and pollution of ground water and nearby surface waters with human fecal pathogens. The State Board of Health gradually adopted rules and enforced the use of septic systems during the mid-1960s to protect public health.

Components of these septic systems included a septic tank with effluent disposal achieved using a drain field or injection well. The porous nature of the Keys substrate limestone results in high nutrient effluent seeping directly into groundwater and adjacent surface waters.

Starting in 1992, the Florida Department of Health required that drain fields be underlined by a minimum 12 inches of clean fill sand (Kruczynski and McManus, 2002).

Although underlying drain fields with clean fill sand provides filtration of pathogens through cat ion exchange entrapment, little or no removal of nutrients such as nitrogen or phosphorus is afforded (Kruczynski and McManus, 2002).

Furthermore, early installed septic tanks were punctured, allowing infiltration of groundwater to prevent groundwater induced flotation of the tanks. This practice short-circuits the system and allows raw sewage to directly contact groundwater (Kruczynski and McManus, 2002).

Deposition of treated sewage or waste-water into the water body affects its quality. For instance, water quality in Florida Bay began showing signs of significant degradation in the late 1980s when such deposition occurred.

Clear water began to turn green and turbid with sea grass die- offs and algae blooms occurring with greater frequency (Dillon etal.,2000). Causes of these ecological changes were hypothesized to be elevated salinity and increased nutrient loading due to the urbanization of the south Florida mainland and the Keys.

Still others suspected natural variability within the ecosystem (Dillon etal., 2000). Coral die- offs, coupled with colonization of benthic algae on dead and dying coral indicated increased nitrification of the coastal waters around the Keys.

When undertaking an assessment of the real cost of employing any given method of waste-water disinfection, it is necessary to consider both human and environmental risks which may be tangible and/or intangible.

Literature clearly reports the potential adverse toxicological impacts of chlorine chemicals and byproducts of chlorination on the aquatic environment (Queensland Department of Environment and Heritage, 1993).

High total residual chlorine in discharges to water may lead to an acute response of aquatic organisms, ranging from avoidance to death. The threshold tolerance limit of some aquatic species to chlorine is 0.002 milligrams per litre in freshwater and 0.01 milligrams per litre in saline water (Department of Environment and Heritage Report QLD, 1991).

Disinfection by-products also have the potential to bio accumulate in the aquatic environment. DE chlorination eliminates the toxicity of the free or combined chlorine residual, but does not effectively reduce other disinfection byproducts.

The beneficial use of aquatic ecosystem protection may be compromised when chlorinated waste- water is discharged to receiving surface waters.

Chlorination should not pose a significant risk to the environment if the treated waste-water is beneficially reused rather than discharged to receiving surface waters. This is an acceptable disinfection method for waste-water reuse.

It should also be noted that chlorination is considered best practice for reuse applications where a residual is required to prevent microbial re-growth and hence re-contamination of distribution and storage systems.

However, there is a limit of one milligram per litre of chlorine at the point of application of reclaimed water. This limit corresponds to the aesthetic threshold and will not usually cause adverse effects on plants.

However, some sensitive crops may be damaged at chlorine levels below one milligram per litre and users should consider the sensitivity of any crops that may be irrigated with chlorine disinfected reclaimed water.

Although the direct use of chlorine for disinfection of reclaimed water should pose little environmental risk, the manufacture, storage and transportation of chlorine products still poses a risk to the environment.

The risk that ozone poses to aquatic organism health requires further research. It has been suggested that the strong oxidation potential of ozone may cause the formation of toxic by-products, but this is yet to be proven.

Ozone gas, however, may adversely impact on surrounding vegetation due to its corrosive and toxic nature. Microfiltration only poses a risk to the environment if there is a spill of cleaning agents or the contaminated backwash waste is disposed of incorrectly.

The potential environmental risks associated with UV are less compared to other methods, but may include photo-reactivation and mutation of the microbial population present in the discharge. There is presently no reuse option for spent UV lamps.

Control over biological disinfection methods, such as detention lagoons, is more difficult as they are natural systems. A significant environmental risk associated with lagoon-based disinfection, is the potential for the excessive growth of undesirable organisms, such as blue-green algae.

Blue-green algal blooms may pose a risk to stock and human health through the production of toxins and to the environment via an increase in SS and BOD levels.

In terms of potential environmental cost, it would appear UV, lagoons and microfiltration has the least potential to impact adversely upon the environment, followed by ozonation then chlorination.

This ranking is based on the potential production of disinfection by products and the potential toxicity of the discharge to the receiving environment.

Treatment Objectives

Satisfactory disposal of waste-water, whether by surface, subsurface methods or dilution, is dependent on its treatment prior to disposal.

Adequate treatment is necessary to prevent mination of receiving waters to a degree which might interfere with their best or intended use, whether it be for water supply, recreation, or any other required purpose.

The purpose or objective of waste-water treatment is generally to remove from the waste-water enough solids to permit the remainder to be discharged to receiving water without interfering with its best or proper use.

The solids which are removed are primarily organic but may also include inorganic solids. Treatment must also be provided for the solids and liquids which are removed as sludge.

Finally, treatment to control odors, to retard biological activity, or destroy pathogenic organisms may also be needed.

The above reasons inform the main aim of waste-water treatment. To achieve the said broad aim of its treatment, some specific treatment objectives must be met, thus given below.

Preliminary treatment-Preliminary devices are designed to remove or cut up the larger suspended and floating solids, to remove the heavy inorganic solids, and to remove excessive amounts of oils or greases.

To effect the objectives of preliminary treatment, the following devices are commonly used:

• Screens – rack, bar or fine
• Comminuting devices- grinders, cutters, shredders
• Grit chambers
• Pre-aeration tanks

In addition to the above, chlorination may be used in preliminary treatment. Since chlorination may be used at all stages in treatment, it is considered to be a method by itself. Preliminary treatment devices require careful design and operation.

Primary treatment – The purpose of primary treatment is to reduce the velocity of the waste-water sufficiently to permit solids to settle and floatable materials to surface. Therefore, primary devices may consist of settling tanks, clarifiers or sedimentation tanks. Because of variations in design, operation, and application, settling tanks can be divided into four groups:

Septic tanks;

• Two story tanks – Imhoff and several proprietary or patented units.
• Plain sedimentation tank with mechanical sludge removal.
• Upward flow clarifiers with mechanical sludge removal.

Secondary treatment– Secondary treatment depends primarily upon aerobic organisms which biochemically decompose the organic solids to inorganic solids. It is comparable to the zone of recovery in the self- purification of a stream. The devices used in secondary treatment may be divided into four groups:

• Trickling filters with secondary settling tanks
• Activated sludge and modifications with final settling tanks
• Intermittent sand filters
• Stabilization ponds

Chlorination – chlorination is a method which can apply in all the stages of treatment. It has been employed for many purposes in all stages in waste-water treatment, and even prior to preliminary treatment. It involves the application of chlorine to the waste-water for the following purposes:

Disinfection or destruction of pathogenic organisms

Prevention of waste-water decomposition – (a) odor control, and (b) Protection of plant structures.

Sludge treatment – The solids from waste-water in both primary and secondary treatment units, together with the water removed with them, constitute waste-water sludge.

Sludge treatment has two objectives – the removal of part or all of the water in the sludge to reduce its volume, and the decomposition of the putrescible organic solids to mineral solids or to relatively stable organic solids. This is accomplished by a combination of two or more of the following methods:

• Thickening
• Digestion with or without heat
• Drying on sand bed – open or covered
• Conditioning with chemicals
• Elutriation
• Vacuum filtration
• Heat drying
• Incineration
• Wet oxidation
• Centrifuging

Tertiary and advanced waste-water treatment – The term tertiary treatment has come to describe additional treatment following secondary treatment. Quite often this merely indicates the use of intermittent sand filters for increased removal of suspended solids from the waste-water.

In other cases, tertiary treatment has been used to describe processes which remove plant nutrients, primarily nitrogen and phosphorous, from waste-water. Improvement and upgrading of waste-water treatment units as well as the need to minimize environmental effects has led to the increased use of tertiary treatment.

In advanced treatment, the degree of treatment is usually achieved by chemical (for example coagulation) methods as well as physical methods (flocculation, settling and activated carbon adsorption) to produce high quality effluent water.

Disposal Regulations

Disposal regulations are sets of standards, rules and regulations that govern the disposal of waste-water, whichever the constituent it contains or it is made of, in the water body or on the land with aim of making sure that the recipient (the water body or the land) does not suffer adversely directly by itself or its content (aquatic or terrestrial/arboreal life).

The question now is: Are there such regulations and how effective are those regulations? A little more and you will be abreast with the true situation of things.

Worldwide, there are laws, acts, and even by-laws that govern the disposal of waste-water with the aim of achieving good healthy living. For instance, in Australia there are acts like:

Environmental Protection Act 1970 – Under the Environmental Protection Act, 1970 discharges to the environment must be managed so they do not adversely affect the receiving environment (that is, land, surface water or groundwater).

At local level, the Public Health Ordinance states that a local or Native Authority may maintain a public sewer within its district. It provides a penalty for any person who introduces refuse or any matter likely to interfere with the free flow of sewage or affect its treatment and disposal.

The Public Health Ordinance lays down the procedure to be adopted by those who wish to connect their drainage systems to the public sewer.

Where a public sewer exists, plans of new buildings must show satisfactory provision for the drainage of the building and connection to the public sewer; also owners of existing building may be required to provide satisfactory drainage in connection with their buildings, provided a sewer is available.

In conclusion, from all that have been discussed above, we can conclude that waste- water impacts negatively on our environment by its being and when disposed on the environment after treatment.

Its presence before treatment spells doom for man and animals as they try to survive from diseases they cause. When discharged into water or on land after treatment, it impacts negatively and positively too. It generally enriches the soil where it is found but may also contain some harmful chemicals that are inimical to plants if they come from industrial wastes.

In order not to do harm much to the environment where waste-water is found and in order to effectively treat same, there is the need to have functional and coordinated treatment goals and objectives. Each stage of the treatment should follow its regular pattern and achieve the specific objective so as to have the overall aim achieved.

Disposal regulations should be made and followed vigorously to make sure that all is well with our environment. At present not much about this is in place.

The definition of the word impact was given before dealing with the impacts waste-water has on the environment where it is found. There is no denying the fact that it has negative effects on the environment which ranges from disease spread, unsightliness to erosion problems in case of storm water.

There are still the impacts of treated waste-water on the disposal site which are dependent on the scope of treatment given before disposal and the nature of the site where the disposal is made.

It may affect the aquatic life if it is disposed into water. It may enrich the soil so much with nitrogen and phosphorous, etc. if it is disposed on the land.

To ensure that negative impacts are not much witnessed and felt, functional treatment objectives must be followed. The major aim of treatment is to ensure that waste-water is not felt adversely by people, animals and plants whether aquatic or terrestrial after treatment and deposition on the land or in the sea. Specific treatment objectives were followed to achieve this.

In order to achieve effective disposal of our waste-water, there is the need to have disposal regulations and standards. These enabling laws will ensure that the aims and objectives of disposals are achieved. There are not many such laws in this part of the world and the few available are not followed to the letter.

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