Contemporary issues in environmental Geoscience with emphasis on water resources

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NREM904.ppt

INSTITUTE OF NATURAL RESOURCES AND ENVIRONMENTAL SUSTAINABILITY

NREM 904: CONTEMPORARY ISSUES IN ENVIRONMENTAL GEOSCIENCE WITH EMPHASIS ON WATER RESOURCES

LECTURER: PROF. G.J. UDOM

  • COURSE
  • NREM 904 contemporary issues in environmental Geoscience with emphasis on water resources assessment and management.

  • CREDIT UNITS

3 Credits

  • CONTENTS

Integrated Water Resources Management; Groundwater Resources Assessment and Management; Wastewater Treatment Technologies; Engineered Sanitary Landfills and Solid Waste Handling; Groundwater Risk Assessment and Remediation; Integrated Coastal Zone Management.

WATER RESOURCES

  • Natural resources of water that are useful.
  • Uses: Agricultural, industrial, domestic, recreational, environmental uses.
  • 97% of water on earth is found in ocean as saline water. 3% only is fresh water, 2/3 of the freshwater is frozen in ice, remaining is unfrozen as groundwater with only a small fraction present above the ground or in the air.
  • Freshwater is a renewable resource, however, groundwater is decreasing in supply particularly in Asia, South America and North America.
  • The framework of allocating water resources to users is known as water rights.

SOURCES OF FRESHWATER

  • Surface water: rivers, lakes, freshwater wetland.
  • Groundwater
  • Frozen water
  • Desalination
  • Brazil, Russia, Canada have the largest supply of freshwater.

WORLD POPULATION

  • Was 6.2 billion in 2000; is estimated (UN) to reach 9.8 billion in 2050.
  • Thus, water demand will continue to increase and there should be a corresponding increase in water conservation and recyling.
  • Water resources should therefore, be properly managed.
  • There will be need to balance access to water with the importance of managing water in a sustainable way, taking into account the impact of climate change and other environmental and social variables.

GROUNDWATER

  • Water found in the zone of saturation where the void spaces are completely filled by water.
  • It is contained in aquifers.
  • Groundwater is preferred to surface water because it can be used without treatment.

GROUNDWATER ASSESSMENT

  • Assessment of groundwater resources yields knowledge necessary for their informed management and governance.

ASSESSMENT OF GROUNDWATER INCLUDES:

  • Hydrogeological characterization.
  • Social, economic and environmental aspects that are needed to understand the resource and its state, in accordance with purpose of the assessment.
  • Groundwater is connected to many goods and services people depend on including food and energy production.
  • Over the years, groundwater situations have changed rapidly due to intensive use of the resource, particularly for irrigation and domestic water supply, coupled with climate change.
  • Changes in quality and quantity can lead to the environmental degradation of the ecosystems.

GROUNDWATER AND ECOSYSTEMS

  • Groundwater plays an integral role in sustaining certain types of aquatic, terrestrial, and coastal ecosystem.
  • The services provided by these ecosystems are therefore also directly or directly dependent on the availability and state of groundwater resources.
  • Increased groundwater abstraction, increased groundwater contamination and climate variability are affecting the functioning of ecosystems and thereby jeopardize the services provided by these ecosystems.

GROUNDWATER MANAGEMENT

  • Sustainable groundwater management means, management of groundwater sub-basins to provide for long-term benefits without resulting in or aggravating conditions that cause significant economic, social or environmental impacts such as long-term overdraft, land subsidence, ecosystem degradation, saltwater encroachment etc.

STEPS IN GROUNDWATER MANAGEMENT

STEP 1

  • Locate and identify water wells, and collect groundwater level, and groundwater quality data. Plot this information on maps for use in steps 2 – 5.

STEP 2

  • Determine the amount of groundwater that is extracted by each well or otherwise removed from the groundwater basin.
  • Total the amount of groundwater extracted by all wells and add whatever other water is removed from the basin (evapotranspiration, exports, consumptive use and surface water outflow).
  • Compare this total to the total amount of water that comes into the basin (see step 4).

STEP 3:

Prepare maps and graphs that show:

  • Past groundwater levels and water quality.
  • Present or recent groundwater levels, groundwater quality, and rates of groundwater extraction.
  • Recent precipitation.
  • Surface water imports.
  • Changes in groundwater levels and groundwater quality and
  • Water exported from the basin.

STEP 4:

  • Determine the total amount of water that flows into the basin through precipitation and surface water imports and the total amount of water that flows out of the basin.
  • This is called water budget.
  • The difference between the inflow and the outflow will result in a change in groundwater level during the water year. If inflow exceeds outflow, groundwater levels will rise and vice versa.
  • INFLOW – OUTFLOW: Change in storage.
  • STEP 5:

Use drillers log and other data to estimate Specific Yield

(Sy):

  • Specific yield is an estimate of the amount of water that is available from an unconfined aquifer.
  • The specific yield can be used to calculated the amount of groundwater in storage, and the decline in groundwater level that will occur when a specific amount of groundwater is extracted by wells (see step 4).

STEP 6:

  • Project future rates of extraction and estimate the rate of decline of groundwater levels and possible changes in groundwater quality.
  • Use the Sy values obtained in step 5 to calculate the estimated change in groundwater level that will occur when an estimated amount of groundwater is extracted.
  • Groundwater quality data can be used to estimate the effect of such extraction on the movement of chemical constituents, either natural or man-made.
  • Determine whether groundwater extraction is likely to cause subsidence. If yes, prepare a subsidence monitoring programme.

STEP 7:

  • Develop a plan for managing groundwater supplies, such a plan may require reduction in extractions so the long-term change in storage does not cause water quality or quantity problems.
  • Such as management plan could include a reduction in the amount of groundwater extracted by specific wells either through a reduced rate of pumping or by restricting the length of time the pump can be turned on.
  • Such reductions would have to be voluntary except enforced by an agency.

WATER POLLUTION CONTROL METHODS

  • Water is the ultimate source and conduit for accumulation and dispersal of environmental pollutants.
  • Therefore the well-being of plants and animals on planet earth is dependent on the quality of water.
  • Different standards are set for different uses of water.
  • However these standards are commonly abused through contamination of water sources.
  • Contamination are commonly from discharge of sewage, organic, biological, industrial and hazardous waste products.
  • Control of water pollution may be achieved by;

Wastewater control and storage.

Avoiding direct discharge of untreated effluents to water bodies and strict adherence to domestic urban and industrial norms of water management protocols.

WASTEWATER TREATMENT PROCESS

  • Wastewater is any water that has been affected by human use.
  • It is used water of domestic, commercial, agricultural source, including storm water.
  • Wastewater can pollute water bodies through chemicals, metals, plant nutrients, waste heats and pathogens.
  • Such contamination can spread infectious diseases or alter physical chemical and biological characteristics of water.
  • Wastewater treatment is thus very necessary before its discharge into water sources.

Water Quality is Shown in the Table Below.

(After Narayanan, 2011)

Substances Undesirable Effects Maximum Allowed Level (mg/L)
Chloride Taste and smell 200
Flouride Fluorosis 1
Phenols Taste 0.001
Detergents Taste and foaming 0.2
Hydrogen sulphide Taste and odour 0.5
Calcium Water hardness 50
Magnesium Water hardness 30
Copper Taste 0.5
Iron Taste and odour 0.1
manganese Taste and odour 0.05
Zinc Taste and odour 5
Ammonia Growth of organism pH 0.05

  • Substances that impair water.
  • Wastewater treatment is necessary to control parameters such as turbidity, DO, BOD, Coliforms, acidity and toxic substances in surface and groundwater upon its discharge.
  • The treatment processes consist of several levels of purification as follows:

Primary treatment

Secondary treatment

Tertiary treatment

  • PRIMARY TREATMENT:
  • At the level of primary treatment, about 60% of suspended solids (SS) and 30% of BOD are expected to be removed,
  • Dissolved impurities are not removed.

  • SECONDARY TREATMENT:

Here about 80% of SS and BOD is removed. In many countries, this is minimum level of treatment required.

  • TERTIARY TREATMENT:

Necessary when a high degree of purification is designed. In addition to total solids and BOD, dissolved impurities like NO3 and PO4 are also eliminated.

  • Nearly 99% of all impurities from sewage are removed.
  • The effluent from tertiary treatment is almost of drinking water quality. Tertiary treatment is expensive.
  • Whatever the level of treatment, the last step in each case is disinfection before discharging the water into a body of surface water.
  • Disinfection is achieved through chlorination or ultraviolent irradiation and ozonation in modern water, treatment plants.

Ultraviolate sterilization refers to the oxidizing and germ killing effects of sunlight.

The application of ozone-unlike that of chlorine-does not produce harmful reaction products such as haloforms.

Excess ozone can easily be decomposed into oxygen.

Due to its high redox potential, the impact of ozone on microorganisms is much stronger than that of any other chemical disinfectant currently in use.

The action of ozone on living cells is believed to be primarily in the form of an oxidative attack on the cell walls which eventually causes the cell to LYSE, i.e. to release its contents.

  • TREATMENT PROCESSES

Primary Treatment: Aims at removing materials that can either float or settle readily under gravity. The processes involve screening, grit removal and sedimentation, pre-treatment for coagulation, flocculation, settling and sludge removal. Finally, a simple post treatment with chlorine.

Wastewater

Screening & Size Reduction

Wastewater

Pretreatment

1st Setting Tank

2nd Setting

Tank

Filtration

Treated

Water

CO2

(pH Adjustment)

Sludge Lagoon

CI2

(Disinfection)

Lime

Coagulation

*

  • Screening
  • Removal of floating material using bar screens (grit removal). The grit chambers slow down the flow of water so that SS (silt, sand, gravel) can settle down.
  • This is followed by the grinding of the solids coming through the screens into size <0.3mm.
  • The floatation – removal of grease and oil.

Pretreatment and Filtration

  • The next step is aeration.
  • The wastewater, free from debris and suspended particles is led into an aeration chamber, where oxidizing agents (chlorine or potassium permanganate) at alkaline pH oxidizes Fe2+ to Fe3+, which hydrolyses and gets precipitated.
  • Addition of lime after aeration raises the pH and precipitates Ca and Mg2+.
  • The precipitate is allowed to settle in the primary basin.
  • Water softening by cation exchange is also used (Na+ ion is exchanged for Ca2+ ion in solution).
  • Coagulants such as alum (ferric and aluminum sulfates) are added to coagulate colloidal suspensions, which are then removed by sedimentation and filtration.
  • ‘Recarbonating’ of water by bubbling CO2 decreases the pH of the water.
  • Settling of precipitate and coagulate is achieved in gravity – settling tanks (2nd basin).
  • The material that settles in the tanks is known as ‘sludge’, which is removed prior to filtration.
  • The treated water is filtered after chlorination and pumped to the city water mains.
  • The sludge from the basin is pumped to a sludge lagoon.

SECONDARY WASTEWATER TREATMENT PROCESSES

  • The objective of Secondary wastewater treatment by biological processes is to remove soluble organic pollutants (carbonaceous materials).
  • The harmful effect of organic matter in wastewater is in the removal of oxygen due to the intervention of microorganisms.
  • Microorganisms consume the organic impurities as food, converting it into CO2, H2O and energy for their growth and reproduction.
  • The same phenomenon is utilized in biological waste treatment.
  • Microorganisms are allowed to degrade organic matter, in solution or in suspension, in the presence of added oxygen until the BOD has been adjusted to acceptable levels.
  • The biological processes depend on pH, T, type of substrate, and the availability of nutrients and minerals.
  • After the organic pollutants are nearly separated and recycled while the purified water is collected for further treatment or pumping to utilities after disinfection.
  • Biological wastewater treatment systems employ AEROBIC and ANAEROBIC METHODS.

TERTIARY WASTEWATER TREATMENT PROCESSES

  • Secondary wastewater treatment reduces suspended matter and BOD, but not nitrogen and phosphorus.
Parameter Raw Wastewater (mg/L) After Primary Treatment (mg/L) After Secondary Treatment (mg/L)
BOD 250 175 15
SS 200 60 15
Phosphorous 8 7 6

  • Tertiary wastewater treatment is an advanced treatment process of the sewage effluents from the secondary treatment process.
  • It removes suspended particulate, dissolved organic compounds, dissolved inorganic compounds that include algal nutrients (N, P), toxic metals and pathogens.
  • Tertiary wastewater treatment includes primary (physical), secondary, (biological) and advanced chemical process.
  • Tertiary treatment is carried out if water of very food quality is required.

REMOVAL OF NITROGEN AND PHOSPHORUS

  • Nitrogen is an algal nutrient. The processes of its removal are:
  • Ion exchange.
  • Reverse osmosis
  • Electrodialysis
  • Air stripping of ammonia
  • Bacterial treatment.
  • Phosphorus is removed from water to reduce algal growth. This can be achieved by:
  • Addition of Coagulants: Lime (Ca(OH)2), alum (Al2(SO)3) magnesium (MgSO4) and ferric salts.
  • Sorption: Pecolating water through a column of activated alumina removes phosphates.
  • Ion Exchange: Water is passed through an anion exchanger bed. Regeneration of ion exchanger is accomplished by NaCl wash.
  • Electrodialysis: By applying a direct current across a body of water separated into layers by membranes alternatively permeable to catious and anions.
  • Reverse osmosis.

INDUSTRIAL WASTEWATER TREATMENT

  • Major pollutants of industrial wastewater include acids, alkalis, inorganic salts, suspended matter, organic compounds and heat.
  • Wastes from pulp, paper, tannery, cannery operation contain suspended and dissolved contaminants.
  • Agriculture veterinary, food and beverges wastes contain suspended and colloidal matter as well as organic matter.
  • Flotation or sedimentation removes suspended solids.
  • Salts may be removed by ion exchange or reverse osmosis.
  • Sludge is removed by filtration.

REMOVAL OF HEAVY METALS

  • Heavy metals such as As, Cd, Cr, Cu, Hg and Pb are removed through various physicochemical processes.
  • Lime or lime with sulfide treatment removes most heavy metals as insoluble hydroxide and basic salts.
  • Removal of toxic metals in water includes processes of precipitation/ coagulation, adsorption, ion exchange and membrane filtration.

SOLID WASTES AND THEIR DISPOSAL

  • Solid wastes consist of garbage, rubbish, trash, industrial and agricultural runoff, animal and human waste, and sewage sludge.
  • Waste disposal protocols involve collection, storage, processing, transport and disposal.
  • Processing includes separation, screening, size reduction, compaction and treatment, incineration etc.
  • The main disposal operation are land filling, composting (biological degradation), incineration (volume reduction) and recycling methods.
  • Incineration is not a total solution as it contributes to atmospheric and thermal pollution.
  • Different solid wastes disposal methods are stated in the Table below.
Process Purpose Waste Disposal
Filtration Dewatering Sludge
Chemical Addition Precipitation Sludge
Landfill Storage and disposal Inert and radioactive materials
Submerged combustion Dewatering Liquids
Incineration Volume reduction Most organic materials
Biological degradation (compost) Dilution Biodegradable organics
Recycling Reuse Metals

LANDFILL

  • Sanitary land filling method is the simplest and widely used waste disposal method of solid, non-hazardous and non-radioactive wastes.
  • Daily solid waste is transported to a landfill site, spread in a layer and covered with a 10 – 20 cm thick soil and a plastic liner.
  • When refuse ‘cells’ in a site are filled, a layer of 0.5m impervious soil, called final cover, is spread on top of the landfill.
  • The geographic and topographic selection of a landfill site is very important.
  • Monitoring and control systems are provided for detecting, and if necessary, elimination contamination of the soil around the pit and underground sources with offensive lachates from the piles.
  • The advantages of a landfill are low cost, flexible operation, and final disposal.
  • Disadvantages include slow process, large land area required, and the possibility of leaching of pollutants and toxic metals from the site into the groundwater.

COMPOSTING

  • This is a biochemical degradation of organic materials (biodegradable trash) under carefully controlled conditions to yield humus – like soil supplement.
  • Composting offers a method of processing and recycling both garbage and sewage sludge in one operation.
  • The volume of the waste can be reduced by as much as 50%.
  • Digested compost is processed and used as mulch.
  • Processing includes drying and screening.
  • The decomposable materials in refuse, are isolated from inorganic materials through sorting and separation operation based on size, density, magnetic and other physical properties.
  • Shredding reduces the size of the waste material to uniform size.
  • Composting can be developed into a major process for handling sewage sludge to maintain an eco-friendly environment.
  • As more stringent environmental rules and sitting constraints limit the use of solid waste incineration and land filling, the application of composting is likely to increase.

INCINERATION

  • Incineration is a controlled combustion process used to reduce and destroy residual organic matter and pathogens.
  • ADVANTAGES ARE:

Application to all combustible (organic) materials.

Suitable to handle biohazard waste.

Large land areas are not required.

  • DISADVANTAGES ARE:

- Environmental nuisance.

Products may be hazardous to health.

It is not the ultimate disposal method, combusted residues still have to be disposed.

  • Modern municipal incinerators are designed to operate on the basis of continuous feeding and burning of the solid waste.
  • Complete burning in any incineration process depends on:

- Combustibility of the pollutants.

Residence time.

Flame temperature and

Turbulence

  • For burning carbonaceous wastes without smoke, temperature > 750oC has to be maintained.
  • The degree of turbulence of the air in the incinerator affects oxidation and it overall performance.

RECYCLING

  • Recycling of part of the solid waste generated in the domestic and industrial sectors is an attractive way of conserving resources as well as reducing the burden on storing and final disposal, for example converting wastepaper from offices into corrugated boxes or newsprint (post-consumer recycling).
  • Recycling involves separation, recovery and reuse of components of solid waste that may still have economic value.
  • Composting and incineration with heat recovery can be considered as recycling technologies.
  • Municipal waste paper, metals, glass, plastics and rubber are reusable materials, at least after some processing.
  • Solid – waste recycling methods are summarized below:
Recycling Process Components
Steam generation Combustible components
Composting Garbage, rags, wood chips and paper
Waste recovery All refuse
Metal recovery All refuse
Gasification and pyrolysis Organic fraction of wastes

RADIOACTIVE WASTE DISPOSAL

Low-Level Radioactive Waste

  • Nuclear industry, nuclear power plants, medical establishments, research facilities and some government organization are the sources of generating low-level radioactive waste.
  • Land disposal is a common practice. This should provide sufficient isolation of waste to protect humans and the environment.
  • Choosing disposal sites takes into account geology, geochemistry, tectonics, surface processes, meteorology, human induced events, transportation of the waste from the point of generation, land use, population distribution and environmental protection.
  • Most facilities for low-level waste disposal are located 10m below the earth’s surface, some in mine cavities > 50m, some in geological repositories hundreds of meters deep.
  • Once a disposal facility is loaded to its capacity, processes known as ‘closure’ and ‘post-closure’ are set into operation.

These consist of:

- Covering or sealing the disposal area.

Preparing documents and performing safety assessments.

  • Several hundred of years are foreseen for post – closure institutional control.
  • This process includes access control, maintenance, site monitoring, record keeping and corrective actions where necessary.

HIGH-LEVEL WASTES (HLW)

  • The disposal of HLW is becoming a matter of serious concern.
  • HLW is a serious threat to anyone who comes near the waste without shielding.
  • HLW comprises uranium, plutonium etc. with isotopes having long half-lives (some longer than 100,000 years).
  • A short-term storage is planned for materials like spent nuclear fuel before a more permanent placement is decided. A ten-year storage is envisaged for temporary storage.

At this stage the material becomes amenable to handling

and shipment.

  • Presently, it cannot be said with certainty that the world or even the countries holding large amounts of these potentially dangerous wastes, have found a long-term, safe solution for their ultimate disposal.

THANK YOU