Essay: Water and wastewater treatment

This coursework incorporates three sections:

1. Understand the Type II settlement column test and analyze it to determine the solids removal efficiency.
2. Elaborate the water treatment strategies and quality tests to be carried out for the two contrast types of drinking water supplies.
3. Elaborate the water quality problems and available treatment approaches because of nitrogen and phosphorus concentrations in wastewater treatment effluents, which also causes eutrophication and other problems.

ABSTRACT (QUESTION – 1)

The aim of this course work (Question-1) is to understand the Type II settlement column test and analyze it to determine the solids removal efficiency.

QUESTION: 1 (a)

TYPE-II COLUMN TEST PROCEDURE

INTRODUCTION

Source: Settling and Floatation ‘ Part 2, web document

• Particles settling in a water column might have affinity towards one other and coalesce to form flocs/ aggregates.
• These larger flocs will have more weight and settle faster overtaking the smaller ones, thereby, coalescing and growing still further into much larger aggregates.
• The small particle that starts at the surface will transforms as a large particle when it reaches the bottom.
• Velocity of the growing flocs will therefore not be terminal (constant or one, but changes as the size changes) ‘ refer fig 1
• Because the particles form into flocs, this type of settling is called flocculent settling or type 2 settling.
• As the velocity is terminal in the case of type I settling; only one sampling port was provided while performing the settling test.
• In an attempt to capture the changing velocity in type 2 settling, often multiple sampling ports are provided.
• The ports closer to the top of the column will capture the slowly moving particles, especially at the end of the settling test.

Fig. 1 ‘ Particle growth with time

Source: Thomas E. Wilson, P.E., DEE, Ph.D et al. (2005) p.150

A batch-type laboratory procedure was developed to estimate the necessary surface overflow rate (SOR), detention time or basin depth, and percent removal of suspended solids. The procedure, described in most of the textbooks is as follows:

• Use a batch-settling column equal to the proposed clarifiers depth and 120mm by 200 mm (5 in. by 8 in.) in diameter, with sampling ports at equal intervals (Fig 2).
• Determine the initial suspended-solids concentration of the suspension under study.
• Mix the suspension thoroughly and transfer the contents rapidly into the column to ensure a uniform mixture. Care should be taken to avoid shearing of particles.
• The procedure should be carried out under quiescent conditions and the temperature within the column should not vary more than 10C (1.80F).
• Samples are collected from each port at selected intervals. The total time that samples are collected should at least equal the detention time of the clarifier.
• The percentage removal of total suspended solids is computed for each sample.
• Percent removal values are plotted as numbers on a set of coordinate axes labeled tank depth (H) on the ordinate and sampling time (t) on the abscissa (Fig 3).
• Curves of equal percentage removal (isopercent curves R1 through R6) are drawn through the points, interpolating where necessary.
• A series of detention times are selected. The percentage removal and SOR corresponding to each are computed according to
  SOR = Vc = H/t

Where

H = the settling column height (m),
t= the detention time selected (min), and
Vc= settling velocity (m/min).

and overall percentage removal, as given by

R = ‘(‘h/H) (Rn+Rn+1)/2

Where

R = overall removal (%),
‘h = vertical distance between adjacent isopercent curves (m),
H = total height of settling column (m), and
RnandRn+1= isopercent curve numbers n and n+1

Fig. 2 ‘ Type II settling column equipment

Fig ‘ 3: Batch settling curves

The overall solids removal at detention time t2 and depth H is

(‘h1/H) (R5+R6)/2 + (‘h2/H) (R4+ R5)/2 + (‘h3/H) (R3+ R4)/2

• Plot computed SOR versus percentage removal. Knowing SOR, percentage removal can be obtained from the graph.
• Adjust the SOR by appropriate scale up factors. As per recommended suggestions the prototype SOR be adjusted as follows:

SOR = Laboratory value Scale up factor (1.25 to 1.75)

As this procedure indicates, settling tanks are typically designed using an SOR, detention period, or both and assuming an ideal settling basin. Scale up factors such as those suggested in the above step is required to compensate for these. However, some effort has been made to examine the reliability of the laboratory test procedure and the influence of some of the factors mentioned.

Temperature is an important factor in type II clarifier design, especially those operating at low solids levels, such as clarifiers following fixed-film processes. Increases in water viscosity at lower temperatures retards particle settling in clarifiers and requires extended detention times to maintain the same removal efficiency.

Zanoni and Blomquist (1975) have examined the repeatability of the laboratory design procedure. They found that column diameter (100 mm versus 150 mm [4 in.versus 6 in.]) and number of sampling ports (four versus seven) produced only minor differences in results. Thackston and Eckenfelder (1972) have presented a procedure modification that accounts for the actual hydraulic regime in the clarifier. However, the method requires a tracer curve from a clarifier with a hydraulic regime similar to the one proposed. Inlet and outlet turbulence in clarifiers reduces the effective settling area.

QUESTION: 1 (b) – i

Determining overall removal efficiency (%) if the retention time is 1hr 20min for a column of size 2.4m deep with initial, fully mixed concentration of solids to be 200 mg/l

Table. 1 ‘ Measured solids concentration (mg/l) during Type II settlement column test

Time of Sampling (minutes)

Depth (m) 20 40 60 80 100 120
0.4 111 69 42 32 25 19
0.8 150 104 78 54 46 36
1.2 169 125 98 78 58 48
1.6 178 140 113 92 75 58
2 183 150 121 103 86 67
2.4 188 157 129 111 94 79

Fig. 4 – Plotted graph
From the above graph,
‘1 = 0.2m
‘2 = 0.2m
‘3 = 0.8m
‘4 = 1.2m

The overall solids removal at detention time t and depth H is

(‘h1/H)((R7+R6)/2) + (‘h2/H) ((R6+ R5)/2) + (‘h3/H) ((R5+ R4)/2) + (‘h4/H) ((R4+ R3)/2)
The overall solids removal at detention time 80min and depth 2.4m is

(‘h1/H)((R7+R6)/2) = (0.2/2.4) ((100+90)/2) = 0.083 * 95 = 7.91 %
(‘h2/H)((R6+R5)/2) = (0.2/2.4) ((90+75)/2) = 0.083 * 82.5 = 6.875 %
(‘h3/H)((R5+R4)/2) = (0.8/2.4) ((75+60)/2) = 0.333 * 67.5 = 22.5 %
(‘h4/H)((R4+R3)/2) = (1.2/2.4) ((60+45)/2) = 0.5 * 52.5 = 26.25 %

TOTAL OVER ALL REMOVAL EFFICIENCY = 63.5 %

QUESTION: 1 (b) ‘ ii

Hydraulic loading rate:

As per recommended standards, typical dimensions of circular sedimentation tank are assumed.

Assumptions:

Diameter, d = 15m
Radius, r = 15/2 = 7.5m
Area = r2
= 3.14 x 7.5 x 7.5 m2
= 176.63 m2
Hydraulic loading rate = Q/A m3/day/m2
Where, Q = 5,000 m3/day taken from the given problem
Therefore, HLR = 5000/176.63
= 28.3 m/day

QUESTION: 1 (b) ‘ iii

Design of circular sedimentation tank of design flow 5000 m3/day

Assumed, the tank dia as d=15m
Where
Q = flow rate (m3/h)
As = surface area, m2
H = depth of water, m
W = tank width, m
L = tank length m
length, t = detention time, hr
V0 = Overflow rate
Vs = Settling Velocity
V0 = Vs = 28.3 m/day
As = 5000/28.3 = 176.67 m2
As = D2/4= 176.67 m2
3.14xD2/4 = 176.67 m2
Therefore, D = 15 m < 40 m

Assume, detention time = 1.33 hrs

H = t*V0 = (1.33*28.30)/24= 1.568m ‘ 1.60 m

Check horizontal velocity at the beginning and end of settling zones:

Vh = Q/( Din H) = 5000/(24*60*3.14*1.6*1.6) = 0.431 m/min (End of inlet zone)

Vh = Q/( DoutH) = 5000/(24*60*3.14*16.6*3.9) = 0.017 m/min (beginning of outlet zone)

Din ‘ H
Dout ‘ H+D

Take weir loading rate = 200 m3/d

L weir = Q/Wload = 5000/200 = 25 m, Use suspended troughs inside the tank.

Available Length = Dtotal = (2H + D) =3.14*(2*1.6+15) = 57.148 m > 40 m — OK

Available W load = Q/L = 5000/57.148 = 87.49 m3/m2 d < 200 m3/d — OK

CONCLUSION

Based on the settling column values and interpolation curves, type II column test analysis has been done and removal efficiency has been calculated. Along with the removal efficiency, hydraulic loading rate is also calculated. Moreover with the hydraulic loading rate, circular sedimentation tank is also designed.

Reference List

• Assist. Prof. Bilge AlpaslanKocamemi, ‘Environmental Engineering Unit Operations’, Lecture [Online]. Available: http://mimoza.marmara.edu.tr/~bilge.alpaslan/enve301/Lectures/Chp_10.pdf [accessed 10 February 2014]
• C. P. PISE, S. A. HALKUDE (2011) ‘A MODIFIED METHOD FOR SETTLING COLUMN DATA ANALYSIS’, International Journal of Engineering Science and Technology (IJEST) [online], Vol. 3 No. 4, ISSN: 0975-5462. Available: http://www.ijest.info/docs/IJEST11-03-04-046.pdf[accessed 13 February 2014]

ABSTRACT (QUESTION 2)

In our coursework (question’2), we are going to elaborate the water treatment strategies and quality tests to be carried out for the two contrast types of drinking water supplies: a) Upland reservoir with pH 5.5 & b) Anaerobic ground water with pathogens & metals like iron and manganese. According to Mr. Noel Bourke et. al, Water treatment manuals, EPA, 2003, pure water is rare to found in nature. Suspended, colloidal and dissolved matters are the three forms of impurities.

INFLUENCE OF RAW WATERSOURCE

Groundwater sources are possibly free from biological contamination by color, plankton or coli form organisms but usually may have high dissolved solids content. Iron and manganese are the common dissolved solids usually present in excess of allowed concentrations for drinking. Water from an upland reservoir may be of good quality with different color due to drainage from peat bogs and will be acidic with poor buffering capacity. Alkali solutions are added with such waters to enhance coagulation and flocculation for removing the color. (Source: Water treatment manuals, EPA, 2003)

The Chalk Aquifer is an important ground water resource in UK. (Source: UK groundwater forum). Pathogenic organisms such as bacteria, viruses, protozoa and metazoan are present in huge quantities in the ground aquifer. Soil acts as the first barrier to pathogen contamination of aquifers (refer fig-1 & 2). Most protozoan and metazoan pathogens like helminthic parasites in addition to other microorganisms are removed by filtration mechanisms. (Source: Brian Morris, formerly of British Geological Survey)

In freshwater, the primary ions are calcium and magnesium; iron and manganese may also contribute. Metal ions are dissolved in groundwater and surface water when the water is exposed to rock or soil containing the metals, usually in the form of metal salts. Metals can also enter with discharges from sewage treatment plants, industrial plants, and other sources. (Source: Frank R. Spellman, 2003)

Fig. 1 – Typical major aquifer situations in the UK (Source: Brian Morris, formerly of British Geological Survey)

Fig. 2 – Groundwater supply pollution pathways by on-site sanitation (Source: ARGOSS manual, 2001)

WATER TREATMENT STRATEGIES:

Basic Water Treatment Processes

(Source: Frank R. Spellman, 2003)
‘ Screening – Removes large debris which shall damage plant equipment
‘ Chemical pretreatment – Conditions the water for algae removal and other aquatic nuisances
‘ Pre-sedimentation – Removes gravel and other gritty materials
‘ Micro straining – Removes algae, aquatic plants, and small debris
‘ Chemical feed and rapid mix – Adds chemicals (coagulants, pH, adjusters, etc.) to water
‘ Coagulation/flocculation – Converts non-settleable or settable particles
‘ Sedimentation – Removes settleable particles
‘ Softening – Removes hardness-causing chemicals from water
‘ Filtration – Removes particles of solid matter which can include biological contamination and turbidity
‘ Disinfection – Kills disease-causing organisms
‘ Adsorption using granular activatedcarbon – Removes radon and many organic chemicals such as pesticides, solvents, and trihalomethanes
‘ Aeration – Removes volatile organic chemicals, radon H2S, and other dissolved gases; oxidizes iron and manganese
‘ Corrosion control – Prevents scaling and corrosion
‘ Reverse osmosis, electro dialysis – Removes nearly all inorganic contaminants
‘ Ion exchange – Removes some inorganic contaminants including hardness-causing chemicals
‘ Activated alumina – Removes some inorganic contamination
‘ Oxidation filtration – Removes some inorganic contaminants (e.g., iron, manganese, radium)

PRETREATMENT

(Source: Frank R. Spellman, 2003, p-492)

Water pretreatment usually includes screening, pre-sedimentation, and chemical addition. Pretreatment process normally consists of oxidation and other treatment for the removal of tastes and odors, iron and manganese, trihalomethane (THM) precursors, or entrapped gases (like hydrogen sulfide).

AERATION

(Source: Frank R. Spellman, 2003, p-492)

Aeration treats water to remove trapped gases such as hydrogen sulfide that causes unpleasant taste and odor. Aeration functions well whenever the pH of the water is less than 6.5. Iron and manganese, oxidizing humic substances that might form trihalomethanes when chlorinated, eliminating other sources of taste and odor, or imparting oxygen-to-oxygen deficient water shall be oxidized by aeration.

COAGULATION & FLOCCULATION

(Source: Frank R. Spellman, 2003, p-502)

The main purpose of water treatment (especially water from upland reservoir) is chemical explication by the processes of coagulation and mixing, flocculation, sedimentation, and filtration. Naturally occurring organic matter (NOM [i.e., bacteria, algae, zooplankton, and organic compounds]), and microbes from water are removed along with disinfection. This process also forms non-corrosive water; particles are also destabilized, agglomerated, dissolved.
Adding salts of iron or aluminum to the water influences coagulation. Common coagulants (salts) are as follows:
‘ Alum (aluminum sulfate)
‘ Sodium aluminate
‘ Ferric sulfate
‘ Ferrous sulfate
‘ Ferric chloride
‘ Polymers

Flocculation forms uniform, feather-like material similar to tenacious floc that entraps the fine, suspended, and colloidal particles and allows them to settle down rapidly in the basin.

SEDIMENTATION & FILTRATION

(Source: Frank R. Spellman, 2003, p-505)

The water containing the floc (because it has a higher specific gravity than water) flows to the sedimentation or settling basin after raw water and chemicals have been mixed and the floc formed, Settle-able solids are removed by gravity during Sedimentation. Through the sedimentation tank or basin, water moves slowly at entry and exit points with minimum short-circuiting with a minimum of turbulence. Sludge is accumulated at the bottom of the tank or basin. Straining, settling, and adsorption are the process involved filtration.

DISINFECTION

(Source: Frank R. Spellman, 2003, p-515)

Chlorine, chlorine dioxide, chloramines, ozone, and potassium permanganate are the most commonly used disinfectants and oxidants that disinfect the water. Destroying all disease-causing organisms in surface water as well as ground water is the primary goal in proper disinfection of a water system.

IRON AND MANGANESE REMOVAL

(Source: Frank R. Spellman, 2003, p-497)

Iron and manganese are normally found in most of the water sources: groundwater and some surface waters. Even though they don’t cause any health issues to human beings, they are likely to cause aesthetic problems, which are objectionable by human beings. Deferrization and demanganization are the normal chemical precipitation treatments for removing iron and manganese. Aeration ‘ dissolved oxygen (DO) in the chemical causes precipitation. Chlorine or potassium permanganate may be required.

TREATMENT OF SOFT WATER

(Source: Water treatment manuals, EPA, 2003, p-14)

Lime or soda ash shall be added with soft waters, where the natural alkalinity is insufficient to react with the coagulants, thus boosting the alkalinity condition of water. Sulphuric acid is neutralized by the alkalinity condition in water to form, together with hydroxide, when sulphates hydrolyze. Hydroxide is the desired end product as it is insoluble, floc forming and heavier than water, and it carries the positive electric charge necessary to neutralize the negative charges of the colloidal particles. To make the optimum pH value for coagulation alkaline chemicals are also added also, if required.

TEST METHODS (DRINKING WATER)

(Source: Frank R. Spellman, 2003, pp.435-443)

DISSOLVED OXYGEN TESTING

Water in a stream produces and consumes oxygen, gaining oxygen from plants because of photosynthesis and from the atmosphere. Since the water in a reservoir or lake runs, it dissolves more oxygen than does still water. Respiration by aquatic animals, decomposition, and various chemical reactions consume oxygen.
The solubility of oxygen is related to pressure and temperature and is actually poorly soluble in water. DO in raw water is the necessary element to support life of many aquatic organisms.
Organic materials that are decomposed in wastewater effluent by microorganisms use oxygen for the process. Storm water runoff from farmland, feedlots, and failing septic systems are some of the other sources of waste that oxygen consuming.
Oxygen is measured in its dissolved form as DO, which is measured in mg/litre. DO levels decline, if more oxygen is consumed than produced, and in such case some sensitive animals may move away, weaken, or die.

BIOCHEMICAL OXYGEN DEMAND TESTING
As mentioned, microorganisms in decomposed organic matter in water consume oxygen and the measure of such oxygen is referred as BOD. Chemical oxidation of inorganic matter is given in terms of BOD. Amount of oxygen consumed by these organisms is measured by a test in terms of BOD for a given period of time (usually 5 d at 20C). Temperature, pH, microorganisms, organic & inorganic materials etc. affects the rate of oxygen consumption in a stream.
DO is directly affected by the amount of BOD in water bodies. Higher BOD represents more oxygen depletion in water bodies. In such cases, only little amount of oxygen will be available to aquatic life. Greater BOD and lesser DO faces the same consequences such as those aquatic organisms become stressed, suffocate, and die. Most river waters have BOD less than 7 mg/L, making dilution unnecessary.
Major sources of BOD include leaves and wood debris; dead plants and animals; animal manure; effluents from pulp and paper mills, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban storm water runoff.

TEMPERATURE MEASUREMENT
The proportion of biological and chemical processes usually depends on the temperature of the water bodies. The oxygen content of the water is normally affected the water temperature. Usually, as the temperature goes up, the oxygen level decreases. The oxygen content is also affected by certain factors such as the rate of photosynthesis by aquatic plants; the metabolic rates of aquatic organisms; and the sensitivity of organisms to toxic wastes, parasites, and diseases.

HARDNESS MEASUREMENT
The amount of calcium and magnesium in the water is normally referred to Hardness. Leaching of rocks adds up calcium and magnesium content with water. The shells and bones of many aquatic organisms as well as the cell walls of aquatic plants have an important content, which is calcium. Plants require magnesium as a primary nutrient and also it is an important component of chlorophyll. When hardness is greater than 150 mg/L, softening treatment may be required for public water systems.

pH MEASUREMENT
pH is defined as the negative log of the hydrogen ion concentration of the solution. This is a measure of the ionized hydrogen in solution. Acidity of basicity of a solution is determined by pH level only. pH influences the chemical and physical properties and the reactivity of almost every component in. It also relates to corrosivity, contaminant solubility, and the water’s conductance. The Secondary Maximum Contaminant Level (MCL) range is set at 6.5 to 8.5.

TURBIDITY MEASUREMENT
Turbidity is a measure of water clarity. The suspended materials in water decrease the light passage through water. Turbidity is caused by a number of materials; both organic and inorganic. The size of these particles varies in the size range of 0.004(clay) to 1.0 mm (sand), which also affects the color of the water. Temperature rises with increase in turbidity because suspended particles have the tendency of absorbing more heat. So automatically DO level decreases as we have discussed in the previous section. Photosynthesis and the relative Do is also reduced due to higher turbidity levels because of less light penetration into the water.

CONCLUSION

The, surface water sources, as in our case – the upland reservoir can be polluted by man and nature; possibilities are high to possess suspended, dissolved organic (plant or animal origin) and inorganic (mineral) material, bacteria, spores, cysts and plankton and also shall be acidic in nature. In the form of metal salts, metal ions are normally dissolved in ground water and surface water; this is done while the water sources are exposed to soil or rock containing the metals. Other sources such as sewage treatment plants, industrial plants, other wastes etc. shall also be responsible for discharging metals into the water. Also, lots of pathogenic organisms that cause water-borne diseases are present in ground aquifer received from various sources.
To treat the upland reservoir with pH of 5.5 we are recommending adding alkali solutions such as lime or soda-ash to increase the pH level and then followed by other water treatment methods like coagulation, flocculation, sedimentation, disinfection etc. to make it suitable for drinking purpose.
For the ground aquifer with pathogenic organisms and with metals such as iron & manganese, process such as deferrization and demanganization shall be carried out along with aeration, coagulation, flocculation, sedimentation, disinfection etc. to make it suitable for drinking purpose.
After carrying the suitable treatments, quality tests as discussed above shall be done to confirm the required quality needed for drinking.

Reference List

• Mr. Noel Bourke, Mr. Gerry Carty, Mr. Gerard O’Leary, Dr. Matt Crowe and Mr. Darragh, 2003, Environmental Protection Agency, Ireland, Water treatment manuals [Online]. Available: http://www.epa.ie/pubs/advice/drinkingwater/EPA_water_treatment_mgt_coag_flocc_clar2.pdf [accessed 15 February 2014]
• Frank R. Spellman, 2003, Handbook Water and Wastewater Treatment Plant Operations, Water treatment manuals
• UK ground water forum [Online]. Available: http://www.groundwateruk.org/downloads/the_aquifers_of_the_uk.pdf [accessed 13 February 2014]
• Pathogens and groundwater (Contributed by Brian Morris, formerly of British Geological Survey [Online].Available:http://www.groundwateruk.org/downloads/Pathogens_and_groundwater_final%20version.pdf; [accessed 13 February 2014]

ABSTRACT (QUESTION – 3)

In our coursework (question’3), we are going to elaborate the water quality problems and available treatment approaches because of nitrogen and phosphorus concentrations in wastewater treatment effluents, which also causes eutrophication and other problems.

INTRODUCTION

Wastewater treatment systems that discharges effluents are one of the major sources of pollution in the global level. These causes several impacts to all living organisms; few to list: death of aquatic life, algal blooms, habitat destruction, debris, short and long term toxicity from chemical contaminants; in combination with chemical accumulation and magnification at higher levels of the food chain (Akpor O. B, IPCBEE vol.20 (2011), p.1)

As per Rachel Leng, 2009, p.1, phosphorus and nitrogen are the two important nutrients that aquatic plants need. Both these nutrients normally are available in limited conditions thus restricting plants. However, humans have the capacity of increasing the concentration of plant nutrients in water bodies, a phenomenon known as ‘cultural eutrophication’ by excessive fertilizer use, untreated wastewater effluents, detergents, accelerating eutrophication beyond natural levels and generating harmful changes to the natural ecosystem.

Cultural eutrophication is mainly caused by human land use, which shall include agriculture/residential/industrial developments (refer figure 1).

 

Figure 1 – Nutrients in manure and fertilizers are transported to lakes, rivers, and oceans. Excessive nutrient inputs result in degradation of water quality, causing the disruption of aquatic ecosystems (Source: Stephen Carpenter et. Al, p.3)

ADVERSE EFFECTS OF EUTROPHICATION

Source: Stephen Carpenter et. Al, Non-point Pollution of Surface Waters with Phosphorus and Nitrogen, p.6

‘ Increased biomass of phytoplankton
‘ Shifts in phytoplankton to bloom-forming species which may be toxic or inedible
‘ Increases in blooms of gelatinous zooplankton (marine environments)
‘ Increased biomass of benthic and epiphytic algae
‘ Changes in macrophyte species composition and biomass
‘ Death of coral reefs and loss of coral reef communities
‘ Decreases in water transparency
‘ Taste, odor, and water treatment problems
‘ Oxygen depletion
‘ Increased incidence of fish kills
‘ Loss of desirable fish species
‘ Reductions in harvestable fish and shellfish
‘ Decreases in perceived esthetic value of the water body

CONSEQUENCES

Source: Michael F. Chislocket. al, 2013, p.1

Dense blooms of noxious foul smelling phytoplankton’s created in the water sources are one of the major contributors of for eutrophication, which on the other hand reduces water clarity and quality (Fig 2). These algal blooms also contribute to growth reduction of aquatic plants, limit light penetration, and causing die-offs of plants in littoral zones. Dissolved inorganic carbon is also depleted with high levels of photosynthesis related with eutrophication, which increases the pH levels during the daytime. DO is highly depleted by microbial decomposition that takes place after the algal blooms die, causing hypoxic or anoxic condition; which automatically lacks sufficient oxygen to support living organisms.

Figure. 2 – Aerial image of a blue-green algae bloom in Lake Okeechobee, Florida; Credits: Karl Havens and Thomas Frazer, 2012, p.2

IMPACTS AND EFFECTS

Source: Conrad C. Lautenbacher et. Al, 2003, p.9

There are a wide range of potential negative effects resulting from eutrophication, and possible subsequent hypoxia, on the health, and goods and services provided directly and indirectly by ecosystems. Some effects include:
‘ Decreased light availability, algal dominance changes, and increased organic matter production. These primary symptoms can further lead to degradation of habitat, altered migration patterns, decreased fishery production, and subsequent economic impacts on industries dependent on ecosystem productivity.
‘ Decreases in swimming, boating, and tourism due to excessive and unsightly blooms of algae. Alterations in these recreational and commercial activities can impact coastal communities vitally dependent on delivery of such ecosystem goods and services.
‘ Nutrient-induced increases in abundance and growth of toxic algae. Associated algal toxins can result in either human and wildlife illness or death if contaminated seafood is consumed or if windborne toxins are inhaled.
‘ Anoxia-induced shifts in biogeochemical reactions, such as reduction of sulfate to sulfide in bottom sediments, resulting in release of hydrogen sulfide. Although the chemosynthetic process turns hydrogen sulfide into a food source for some bacteria, it is toxic to most forms of marine life.

NUTRIENT REMOVAL FROM WASTEWATER

Municipal and Industrial Treatment Plants

Source: Conrad C. Lautenbacher et. Al, 2003, p.40

On average, secondary treatment does not effectively remove nutrients. Advanced treatment technologies include a wide range of physical, chemical, and biological methods, with nutrient removal rates of 90 percent or greater depending on the specific technology. Systems involving land application and reuse of effluent can reduce these levels even further.
A high level of engineering and maintenance is generally required to achieve significant nutrient removal reductions. Conventional physical/chemical/biological treatment technologies rely on the controlled use of chemical and mechanical energy within engineered structures. These technologies have proven successful in treatment of wastewater, especially systems with controlled flow inputs. Many of these processes are, however, expensive and labor intensive. Chemical addition with primary clarification and biological nutrient removal are the primary methods of removing over 90 percent of the phosphorus from wastewater. Nitrogen is most frequently removed through nitrification/ denitrification processes, while phosphorus can be removed using chemical addition and biological treatment processes. The resulting sewage sludge can be treated and land applied as bio-solids, land filled, or incinerated. The levels of phosphorus in wastewater (and the resulting treatment costs) have been significantly reduced when states or local governments have required the use of low phosphate and no phosphate detergents.

Storm Sewers and Combined Sewer Overflows

Source: Conrad C. Lautenbacher et. Al, 2003, p.41

Storm water from landscaped areas and impervious surfaces (e.g., rooftops, parking lots, and city streets) can result in nitrogen loads to local waterways during rainstorms. Nitrogen from CSOs can be removed using source reduction or treatment. Source reduction through education is one of the most effective means to reduce nutrient inputs. Street sweeping via modern street sweepers also can be effective in reducing phosphorus loads, since matter containing phosphorus is disposed of in a landfill instead of washing into a storm sewer. Structural practices, such as bio-retention and constructed wetlands, reduce both nitrogen and phosphorus discharges into water bodies. Runoff volumes and peak flows can be controlled through the use of retention or holding ponds, reducing stream channel bank cutting and incision that can cause increases in the detachment and mobilization of soils containing phosphorus. Instead of impermeable asphalt or cement, parking lots and other large paved areas could be constructed using permeable membranes. These allow water to percolate through them into the ground instead of draining into storm sewers.
Separation of domestic wastewater systems from storm water flows is the most effective method to reduce untreated discharges, but the cost is often prohibitive. A somewhat less expensive option is to increase the in-line and off-line water storage capacities of the combined sewers, so storm overflows become less common. This stored wastewater can then be treated through the municipal treatment plant when the plant can adequately handle it.

Few Mitigation Strategies

Source: Conrad C. Lautenbacher et. Al, 2003, p.10

a) Urban and Suburban
‘ Lessening nutrient inputs to storm sewers and sewer overflows
‘ Decreasing fertilizer application and runoff from lawn and landscape care
‘ Promoting proper disposal of pet and wildlife waste
‘ Reducing nutrient discharges from municipal and industrial water treatment plants

b) Agricultural
‘ Decreasing fertilizer application rates and optimizing its use
‘ Encouraging alternate tilling methods and cropping systems
‘ Improving treatment and disposal of animal waste
‘ Promoting the use of conservation buffers (e.g., field borders, riparian zones, wetlands, and other areas particularly effective at trapping nitrogen) and other physical mechanisms to decrease direct agricultural runoff to water bodies

c) Atmospheric sources
‘ Cooperatively applying air quality provisions regionally
‘ Increasing fuel efficiency of combustion engines
‘ Considering the dispersal patterns of atmospheric discharges from power plants and other industrial sources
‘ Using alternative power sources with lower NOx emissions
‘ Decreasing NOx emissions

Reducing Agricultural Sources

Source: Conrad C. Lautenbacher et. Al, 2003, p.42

Over the past half-century, advances in crop and soil sciences have led to improved management strategies and technologies that increase agricultural productivity. Chief among these advances has been nutrient management strategies to provide essential nutrients for crop growth. While dramatically increasing agricultural productivity, these advances have also had adverse environmental impacts, as manifested through increased nutrient delivery from agricultural lands to surface water and groundwater.

Reducing Atmospheric Loads

Source: Conrad C. Lautenbacher et. Al, 2003, p.46

Fortunately, because NOx emissions are a primary contributor to ozone and smog in the lower atmosphere and to acid rain across the Nation, controlling them has received substantial study. Activities that focus on meeting the ozone standard can also result in reductions in nitrogen deposition. These include transportation changes, such as reductions in growth of vehicle miles traveled through increases in public transportation, or restrictions on emissions from local point sources.

Organic farming

Source: B. ZANOU and A. KOPKE, 2001, p.7

Organic farming generally improves the quality of the landscape, biodiversity and the management of nitrate pollution. All unhealthy life styles are due to the intake of poisoned food, which results from agriculture with pesticides, insecticides, inorganic fertilizers etc. Such poisons reach water bodies by runoff, cohesion, precipitation etc. Organic farming is the ultimate source to reduce such pollution and to protect the water bodies as well as all living organisms and the environment. It is assumed that organic farming practices (by olive farmers) lead to zero emission levels of nitrates and phosphates. To achieve an overall emission reduction of 30% for nitrates and 10% for phosphates into the Gulf, half of all farmers would have to convert to organic farming practices

Use of Aquatic Macrophytes ‘The Green Liver Concept’

Source: Pindihama, G. K et. al, 2011, p.4

Plants growing in lakes, ponds and streams are called macrophytes. These aquatic plants appear in many shapes and sizes. Some have leaves that float on the water surface, while others grow completely under water. Any of these macrophytes are potential candidates for in-situ bioremediation of cyanobacterial toxins found in freshwater bodies. Aquatic macrophytes have mainly been employed in remediation of (removal) of heavy metals. Nymphaea nouchalia (blue water lilly) and Persicaria decipiens (slender knotweed) have been identified as possible candidates as these are dominant and well adapted for the environment. They have also been used in removal of nutrients (nitrogen and phosphorous) in nutrient rich freshwater. Organic pollutants can also be de-graded chemically and ultimately mineralized into harmless biological compounds by plants. Numerous endogenous activities in plants give them the ability to synthesize, rearrange and detoxify the most complex array of biochemical and biopolymers of any living organisms.

THE FUTURE

Source: Conrad C. Lautenbacher et. Al, 2003, p.14

Any response to the ecological and economic dangers of eutrophication and hypoxia must include continued research and monitoring. These include research on the characteristics that govern estuary susceptibility and adaptability, the factors that determine nutrient loading from various land areas, the quantification of economic and social impacts of nutrient pollution, the development of better monitoring systems, the evaluation of existing mitigation strategy effectiveness, and the development of new mitigation strategies.
Response strategies should be undertaken through an adaptive management structure, focused on watersheds and based on comprehensive site-specific and national monitoring and assessments. Such an approach should be focused on protecting healthy ecosystems and restoring those that have been damaged, rather than a national goal of nitrogen reduction per se. This approach requires active participation of state, local, and regional managers leveraged by support and coordination from the Federal government.

CONCLUSION

Nutrients, particularly nitrogen, pose the largest pollution threat to the estuaries. There are a variety of sources of nitrogen, including natural sources, runoff from agricultural fields, concentrated animal feeding operations, and atmospheric deposition of NOx from fossil fuel combustion, and sewage and septic wastes. Negative effects of excessive nutrients, such as algal blooms and hypoxia, have been observed in a significant number of the estuaries. The most effective approach to managing this issue is one that targets the protection of healthy ecosystems and restoration of damaged ones. Three key areas requiring attention are: developing a more comprehensive monitoring program to take advantage of existing programs and explore real-time data acquisition and remote sensing monitoring approaches, improving models of the movement of nutrients through watersheds in response to natural and human activities, and developing estuarine susceptibility models capable of forecasting the impact of changes in nutrient loads.

Reference List

• David L. Russell, Global Environmental Operations, Inc., Lilburn, Georgia 2006, Practical Wastewater Treatment
• Rachel Leng, 2009, The Impacts of Cultural Eutrophication on Lakes: A Review of Damages and Nutrient Control Measures [Online]. Available: http://twp.duke.edu/uploads/assets/Leng%281%29.pdf; accessed [09 February 2014]
• Stephen Carpenter Chair, Nina F. Caraco,David L. Correll, Robert W. Howarth,Andrew N. Sharpley, and Val H. Smith, Nonpoint Pollution of Surface Waters with Phosphorus and Nitrogen, Issues in Ecology, (online). Available: http://www.esa.org/esa/wp-content/uploads/2013/03/issue3.pdf; accessed [09 February 2014]
• Karl Havens and Thomas Frazer, 2012, Rethinking the Role of Nitrogen and Phosphorus in the Eutrophication of Aquatic Ecosystems, University of Florida, [online], Available: http://edis.ifas.ufl.edu/pdffiles/SG/SG11800.pdf; accessed [05 February 2014]
• Michael F. Chislock (Department of Fisheries and Allied Aquacultures, Auburn University), Enrique Doster (Department of Animal Sciences, Auburn University), Rachel A. Zitomer (Department of Biological Sciences, Humboldt University) & Alan E. Wilson (Department of Fisheries and Allied Aquacultures, Auburn University), 2013, Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems [online], Available: http://www.nature.com/scitable/knowledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466; accessed [19 February 2014]
• Akpor O. B., 2011. 3rd International Conference on Chemical, Biological and Environmental Engineering, IPCBEE vol.20, [online], Available: http://www.ipcbee.com/vol20/16-ICBEE2011E20001.pdf; accessed [17 February 2014]
• B. ZANOU and A. KOPKE, 2001, Cost-effective reduction of eutrophication in the Gulf of Kalloni (Island of Lesvos, Greece), Mediterranean Marine Science Vol. 2/1, 2001, 15-25, [online], Available:http://www.google.ae/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&ved=0CE4QFjAG&url=http%3A%2F%2Fwww.medit-mar-sc.net%2Findex.php%2Fmarine%2Farticle%2Fdownload%2F272%2F255&ei=gfsOU83aH6Pv0gWU-oDIAg&usg=AFQjCNGEJdXpA7995877d7ssfMA8YIuUJw&bvm=bv.61965928,d.d2k; accessed [17 February 2014]
• Pindihama, G. K Gumbo, J. R., and Oberholster P. J, 2011, Evaluation of a low cost technology to manage algal toxins in rural water supplies [online], Available: http://www.academicjournals.org/article/article1380894661_Pindihama%20et%20al.pdf; accessed [17 February 2014]
• J.R. Benemann, J.C. Van Olst, M.J. Massingill, J.C. Weissman and D.E. Brune, The Controlled Eutrophication Process: Using Microalgae for CO2 Utilization and Agricultural Fertilizer Recycling, [online], Available: https://www.csupomona.edu/~biodiesel/ref/algae_salton_sea.pdf; accessed [12 February 2014]
• Conrad C. Lautenbacher et. Al (National Science and Technology Council Committee on Environment and Natural Resources), 2003, An Assessment of Coastal Hypoxia and Eutrophication in U.S. Waters [online], Available: http://oceanservice.noaa.gov/outreach/pdfs/coastalhypoxia.pdf; accessed [22 February 2014]
• C.P. Mainstone , R.M. Dils , P.J.A. Withers, 2007, Controlling sediment and phosphorus transfer to receiving waters ‘ A strategic management perspective for England and Wales, [online], Available: http://www.sciencedirect.com/science/article/pii/S0022169407006221#; accessed [20 February 2014]
• A.C. Edwards, P.J.A. Withers, 2007, Transport and delivery of suspended solids, nitrogen and phosphorus from various sources to freshwaters in the UK, [online], Available: journal homepage: www.elsevier.com/locate/jhydrol; accessed [20 February 2014]
• Lucia S.Herbeck a,n, DanielaUnger a, YingWub, TimC.Jennerjahn, 2012, Effluent, nutrient and organic matter export from shrimp and fish ponds causing eutrophication in coastal and back-reef waters of NE Hainan, tropical China, [online], Available: journal homepage: www.elsevier.com/locate/csr; accessed [25 February 2014]