What Do You Do with Waste?
Waste can be either solid or liquid material.
Solid waste is typically disposed of in land fill; or recycled. This may sometimes be expensive and difficult to manage; but at least most of the time, it will stay where it is put, or not impact on places too far from where it is placed.
Liquid waste can be more of a problem, because it is more likely to move; and when it moves, it can carry other things with it.
- In undisturbed forest about 2% of rainfall runs off the surface into creeks and streams. It may have a bit of debris in it (e.g. twigs or leaves), but is otherwise cool and clear.
- In areas where land is cleared for farming or agriculture, about 14% of water runs off. Clearing land leaves soil exposed, so it is easily eroded. Increased volumes of surface runoff erode river beds and banks, releasing even more soil into waterways.
- In urban regions there are large areas of impermeable surfaces (e.g. paving, roadways, and buildings). Around 85% of surface water runs off from these areas.
- Dirt, litter, oil, garden chemicals and animal wastes are carried with the run-off water into drains and eventually streams, and then estuaries and bays.
- For example in Melbourne, Australia there are an estimated 200,000 side entry drain pits in roadside kerbing, where litter and other debris (e.g. soil, plant matter) can enter the storm-water system
- With much higher runoff, and large areas of impermeable surfaces there may be less water entering groundwater systems in lower catchment areas, although this may be offset by increases to groundwater as a result of cleared vegetation in upper and middle catchment areas.
Many major cities have two separate water removal systems:
- Sewage (this will be directed through treatment systems/plants of some sort)
- Storm water (rarely passing through any sort of treatment system). The storm-water system is designed to move large volumes of water quickly to prevent flooding, but as a result it also collects and transports huge amounts of contaminants. Illegal connections of storm-water pipes to sewage pipes can cause overflowing of sewerage through overflow pipes out into the environment (e.g. creeks) which can cause major pollution.
How Can We Clean Up Storm-water?
There are a number of ways in which residents can help to keep storm-water clean. This includes understanding the sources of pollutants, and adopting design principles which help prevent pollution. This is also called "water sensitive design". Examples of such design include:
- House and street designs that retain water on site and encourage absorption into the ground.
- Creation, reclamation or enhancement of wetlands. These can help retain water on site, use up nitrates and phosphates leached from the soil or washed in surface water, provide valuable wildlife habitat, as well as being aesthetically pleasing.
- Irrigated tree plantations, using runoff water, on large industrial sites.
- Diverting runoff from factory, warehouse or shopping centre roofs to feed
- Xeriscape gardens - this involves the use of plants that don't require supplementary watering. This reduces the need to utilise valuable water supplies, and can greatly reduce water runoff from irrigation activities.
- Design for water efficient gardens, such as drip or trickle irrigation systems instead of sprinklers or hand held houses, and mulching garden beds.
- Establish treatment plants for storm-water as we do for sewerage. This is an expensive option.
Reducing Pollutants in Storm-water
In response to the ever increasing litter, pollution and contaminants prevalent in the storm water system in the USA, the USEPA (United States Environment Protection Agency) has developed a storm-water management program (Phase11) that has been implemented nation-wide. Each city, town, village etc throughout the nation are required to implement the six-part program to reduce pollutants in storm–water runoff to the maximum practicable extent. The program must include:
- Public education
- Public involvement programs
- The detection and elimination of illicit and illegal connections.
- The control of construction sites of more then 1 acre.
- Controls for re-developments and new developments.
- Pollution prevention and good house-keeping practices of the storm-water system within each community.
Water-borne litter is a problem world-wide. The effect of aquatic litter goes beyond the despoiling of local environments; it has global implications - for example: thousands of tonnes of water borne litter from London are carried by currents and tides into the North Sea and beyond annually.
Although current practices to remove litter include in London for example: Marine Services operated driftwood collection vessels, a tug and fleet of barges, skips, baskets, rubbish containers as well as passive debris collectors in the river; Local government is still vague on where the responsibility for removal of aquatic rubbish lies.
In the USA as part of their Phase 11 program mentioned earlier systems for water carried litter have been introduced that include: Catchment nets, filters, pollution and sediment screening and water treatment i.e. UV treatment for contaminants.
In the city of Melbourne, in Victoria, Australia, for example 4.5 million pieces of litter per year float down the waterways. This doesn't include things such as plastic bags that move below the water surface. An estimated 540 million plastic shopping bags are disposed of each year in Melbourne. Even 1% of these entering Melbourne's streams amounts to 5.4 million bags. Surface booms (e.g. on the lower reaches of the Yarra River), and litter traps on storm-water drains can have a big impact on the amount of rubbish reaching the bays.
In the state of Victoria alone, millions of dollars is spent per year removing litter from lakes and waterways. A lot of this money is spent removing litter from beaches. A targeted litter survey carried out in Melbourne found that 90% of the litter in the bays, rivers and on the beaches of Melbourne was washed there via the cities storm-water system. It was also found that the majority of litter on Melbourne's beaches was not left there by beach users, but was washed down into the bays by streams.
Washing driveways, paths and roads (e.g. roadside kerbs) flushes a lot of debris down the storm-water system. You wouldn't wash that sort of stuff into your pool, so why wash it into our storm-water systems, and eventually into our streams, bays and estuaries?
Some Local Councils have mechanised road sweepers that periodically sweep roadside kerbs clean, but this rarely occurs at frequent intervals, so much of the debris/litter reaching the road ends up in the storm-water system.
Nutrients in Storm-water
Nutrient rich overflows from septic tanks can be a major problem in many cities. Animal droppings, plant wastes, fertilisers, and pesticides are a significant source of nutrients in storm-water. Most home gardeners, for example, over fertilise, or use inappropriate forms of fertiliser. A lot of the plant waste from gardens can be composted and used in the garden as compost or mulch. In some cities, tens of tones of dog droppings are deposited and leach into storm-water each year.
Although pollutants to water run-off by agricultural activities (fertilisers, herbicides etc.) have a significant contributing factor urban run-off is a critical source of pollution particularly in city water-ways. Also in most cases storm-water collected from urban areas is left untreated and is merely discharged into the nearest lake, river or sea.
Detergents containing phosphates that are used to wash cars are also a problem because these phosphates then also enter the waterways.
Using the City of Melbourne as an example; nutrients released from the Werribee Sewerage Treatment plant, which treats much of Melbourne's sewerage, are a significant part of the nutrient load reaching Port Phillip Bay. The Yarra River puts out about the equivalent of one - quarter of the treatment plant's output, however new technologies are (and will further) significantly reduce the amount of nutrients being released to the bay by the treatment plant. In contrast the water from the Yarra is not treated, and significant efforts will need to be made to reduce the amount of nutrients carried into the bay by the Yarra river (not as easy to come to grips with). Likewise, similar problems occur with nutrient loaded discharges from sewerage farms and rivers in most major cities.
Excess nutrients can cause algal blooms. This can seriously deplete levels of dissolved oxygen in the water where the blooms occur, affecting marine organisms. The coastal waters adjacent to some of the world's cities are so polluted that there is a real health risk associated with the consumption of marine organisms, including fish, taken from them.
E.coli and other bacteria can also be a problem (particularly as a result of animal wastes entering our water bodies). Generally levels of E-coli in bays and rivers of major cities are a problem. In the River Thames (London) for example has highly dangerous levels of E-coli and other harmful bacteria, due to large raw sewage discharges from overflows and effluent discharges from sewage plants. In the Yarra River (Melbourne) E-coli have been dropping in the past 20 years however there are times when amounts of E. coli can reach levels that can seriously affect human health.
Toxins in Storm-water
Other toxins can also cause major problems. These include: petroleum products, pesticides, heavy metals automotive products (e.g. tyre rubber, brake linings, rust, plating, antifreeze, etc.). Consider:
- One litre of oil is enough to pollute one million litres of water.
- Shellfish can concentrate background levels of toxicants many thousands of times.
- In many of the world’s large cities, storm-water is the big problem. Most industrial discharges go into the sewerage system. Illegal dumping of industrial wastes can still, however cause major environmental damage.
All rivers and streams will deposit sediments into the bays and estuaries they enter. Some will have naturally high sediment loads and many will have increased sediment loads due to human activity that results in increased levels of erosion, in their catchments. Sediments can cut light to aquatic plants, smother sea grass beds, clog wetlands, and reduce the flow of rivers (blocking). Oil and toxic chemicals can cling (bond) to sediments, and in doing so harm aquatic life.
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