Treatment of Wastes

Treatment of Wastes
Chemically, physically or biologically

Disposed or discharged without harm to the environment

Range of processes – depend on nature of the particular waste

INCINERATION
Is a solid waste treatment technology involving burning waste at high temperature

Thermal treatment

Is a controlled process that uses combustion to converts a waste to a less bulky, less toxic, or less noxious material -Co2, water, ash

i.e. converts the waste into heat (that can be used to generate electricity), gaseous emissions (CO2)to the atmosphere and residual ash.

Pollution

ash
emission to the atmosphere of combustion product gases and particulate matter

Gaseous emissions

The combustiont gases exhausted to the atmosphere by incineration are a source of concern

Main pollutamts in the exhaust gases include acid gases – hydrogen chloride, sulphur dioxide, nitrogen oxides and carbon dioxide

The most serious environmental concerns
wastes that it produces significant amounts of dioxin and furan emissions to the atmosphere.
Dioxins and furans are health hazards


Emission control designs

The quantity of pollutants in the emissions from lincinerators

reduced by a process known as scrubbing - lower concentrations to acceptable levels before atmospheric release

Solid outputs

produces fly ash and bottom ash
amount of ash produced -ranges from 15% to 25% by weight of the original quantity of waste
fly ash amounts to about 10% to 20% of the total ash
The fly ash, by far, constitutes more of a potential health hazard than bottom ash
fly ash contains toxic metals such as lead, cadimium, copper and zinc as well as small amounts of dioxins and furans

Advantages of incineration

burning wastes in a controlled manner
best known method for treatment of clinical wastes and certain hazardous waste where pathogens and toxins must be destroyed by high temperatures.
large expensive land areas are not required

Disadvantages of incineration

equipment is costly to operate
not always a means of ultimate disposal
gaseous and particulate products - hazardous to health

COMPOSTING
Composting is the process of producing compost through aerobic decomposition of biodegradable organic matter

The decomposition is performed primarily by aerobes

This decomposition occurs naturally in all but the most hostile environments, such as within landfills or in extremely arid deserts, which prevent the microbes and other decomposers from thriving

Composting can be divided into the two
areas

Home compositing

Industrial compositing


Composting is the controlled decomposition of organic matter.

composer provides an optimal environment in which decomposers can thrive
a compost pile needs the correct mix of the following ingredients:

Carbon
Nitrogen
Oxygen (from air)
Water

Decomposition happens even in the absence of some of these ingredients, but not as quickly or as pleasantly.

For example, vegetables in a plastic bag will decompose, but the absence of air encourages the growth of anaerobic microbes that produce disagreeable odors, degradation under anaerobic conditions is called anaerobic digestion)

The goal in a composting system

is to provide a healthy environment and nutrition for the rapid decomposers, the bacteria

most rapid composting occurs with the ideal conditions

moisture content - 50 - 60 %
C/N ratio – 25-30:1
temperature – 20-40 oC
pH - 6 - 7.5
oxygen

Materials for composting

all biodegradable material will compost

substances such as non-vegetarian animal manures and bedding, by-products of food production and processing, restaurant grease and cooking oils, and residuals from the treatment of wastewater and drinking water.

Composting will also break down petroleum hydrocarbons and some toxic compounds for recycling and beneficial reuse

most commonly referred to as a form of bioremediation

High-carbon sources provide the cellulose needed by the composting bacteria for conversion to sugars and heat

High-nitrogen sources provide the most concentrated protein, which allow the compost bacteria to thrive

Composting techniques
Different techniques for composting all
employ the two primary methods of
aerobic composting:

Active composting

allows the most effective decomposing bacteria to thrive

kills most pathogens and seeds, and rapidly produces usable compost

Passive composting

lets nature take its course in a more leisurely manner and leaves many pathogens and seeds dormant in the pile

Composting systems

enclosed
home container compositing
industrial in-vessel compositing

in piles
industrial windrow compositing

Home composting

passive composting

throw everything in a pile in a corner and leave it alone for a year or two

active composting

monitoring the temperature, turning the pile regularly, and adjusting the ingredients over time

Microbes and heating the pile

compost pile - kept about as damp as a well wrung-out sponge

provides the moisture that all life needs to survive

Mesophilic bacteria enjoy midrange temperatures, from about 20 to 40 °C

As they decompose the organic matter, they generate heat, and the inner part of a compost pile heats up the most.

The heap should be about 1m wide, 1 m tall

Provide suitable insulating mass to allow a good heat build-up as the material decays

ideal temperature is around 60 °C

kills most pathogens and weed seeds

provide a suitable environment for thermophiic (heat-loving) bacteria, which are the fastest acting decomposers

The centre of the heap can get too hot



Industrial composting

as an alternative form of waste management to landfill

industrial composting or anaerobic digestion can be combined with mechanical sorting of mixed waste streams

Industrial composting helps prevent global warming by treatment of bidegradable waste before it enters landfill

Once this waste is landfilled it breaks down anaerobically producing landfill gas that contains CH4, a potent greenhouse gas


active composting techniques

achieved by composting inside an enclosed vessel which is monitored and adjusted continuously for optimal temperature, air flow, moisture, and other parameters

Compost windrow turners
In-vessel

industrial composting systems

used by a few urban centers around the world

The world's largest composter is in Edmonton, Alberta, Canada

which turns 220,000 tonnes of residential solid waste and 22,500 dry tonnes of biosolids per year

into 80,000 tonnes of compost using a facility 38,690 square metres in size