Archive for November, 2008

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Edible landscapes

November 23, 2008

WATER WISE

Value for landscape

S. VISHWANATH

Edible landscaping can transform a non-functional water guzzling landscape into a functional, bountiful one



Need of the hour: Every city must have such spaces

Conventionally, landscapes have meant large grass lawns with a few plants thrown in to cater to an aesthetic sensibility which assumes that the front of the office or an industry or around apartments should look a certain way. Huge amounts of water are then thrown to keep this grass green and especially in summer time the amount of water use increases dramatically. It may take 10 litres of water per square metre or more to cope with bad sprinkler systems and evapo-transpir ation. A gardener is then appointed to take care of this landscape and usually he takes care of one acre of land.

Water-efficient landscapes

Choosing the right palate of plants, typically native species, usually results in a more water-efficient landscape. The use of water-spreading devices such as sprinklers, micro-sprinklers and drip irrigation systems is also one method of water conservation and water efficiency. The more environmentally aware people and institutions put in place waste water treatment systems to reuse water for landscape purpose. This reduces or eliminates the use of scarce fresh water resources for essentially a non-potable secondary use.

Xeriscaping is one other method where plants such as xerophytes attuned to arid climatic conditions are used to make do with low amounts of water. Plants such as bougainvillea have also been used in water-efficient landscapes to add water efficiency, low maintenance and colour to the landscapes.

Speciality of growing ragi

One form of landscaping which can add value in an era of water, food and fertilizer scarcity is edible landscaping. Imagine a landscape of an acre with Bermuda or Mexican grass. Suppose this was to be converted to a ‘ragi’ (finger millet) field, the same area could generate 8,000 to 10,000 kg. of ragi or millet every year. This is an edible landscape. If one has surplus treated wastewater and a zero discharge policy, then it would be possible to grow rice.

Advantages

Water is fast becoming a scarce resource. Food too is becoming costly. Many people are paying attention to the ‘virtual water’ embedded in food. If a kilogramme of rice has to be grown, it needs 3000 litres of water or more. Most institutions have canteens and need vegetables and grains. Apartments too have families and kitchens. The virtual water flow through these spaces is very high. An edible landscape would provide fresh food, vegetables and grains with the same water demand as for a normal landscape or perhaps less and with the same number of person hours.

Edible landscapes also bring inhabitants with the cycle of nature and the seasons. The month in which ragi or rice has to be planted, the months required for the plants to mature, the system of harvesting and threshing all these are on constant display and are an education to an urban populace not necessarily familiar with how their food is grown.

Gardeners employed from a rural background are usually familiar with edible landscapes and more so with the growing of grains and fruit trees and vegetables than with grass. Imagine your own freshly grown vegetables and fruits, organic to boot, taking care of your wastewater and compost on site and converting vacant spaces and gardens into fields and fruit bowls. Medicinal, aromatic and herbal plants can also be grown.

Edible landscaping can transform a non-functional water guzzling landscape into a functional, bountiful one. What is required is lateral thinking and a bit of water wisdom.

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DEWATS-Decentralized wastewater treatment systems

November 23, 2008

WATER WISE

DEWATS to the rescue

S. VISHWANATH

A look at an efficient method of treating wastewater

Over 80 per cent of water consumed in flats and buildings comes out as wastewater. In un-sewered areas, the conventional practice has been to use a septic tank as the recipient of wastewater flows and the liquid effluents then emerging being led into soak pits or leaching trenches. This form of treatment is insufficient to render the outgoing effluents pollution free; in high water table areas, septic tanks can cause contamination of groundwater and surface water.

Cleaning septic tanks too is a cumbersome and unpleasant affair. There has been continuous work to find better systems of decentralised treatment of sewage. Domestic wastewater has a high percentage of nitrogen and carbonaceous materials as well as bacteria but is relatively simple to treat as compared to industrial wastewater. The world over, focus is on shifting to decentralised methods of treating wastewater which are simple to operate and economical too.

Low on maintenance

One approach being tried globally is called DEWATS or Decentralised Wastewater Treatment Systems. It aims to use local materials in design while following rigorous technical norms. It tries to be as low in energy intensity as possible and in favourable circumstances the whole treatment process of wastewater can be completely gravity driven without any energy requirement at all. This means that power cuts and load shedding or even accidental switching off of motors or pumps does not come into the picture at all, something which has been the bane of traditional wastewater treatment systems. Wastewater flows as low as 100 litres or 1 cubic metre to as high as 1,000 cubic metres can be handled by DEWATS systems. There is very little or no maintenance though the performance has to be monitored regularly.

A typical system for a domestic household consists of a primary treatment system consisting of a settling and floating tank, a secondary treatment system of an up-flow type baffled reactor which digests wastewater anaerobically, a tertiary treatment in subsurface horizontal flow sand filters with reed beds, and, finally, a polishing pond for oxygenation and UV disinfection from the sun’s rays.

Effective

The treatment of wastewater is highly effective and consistently meets pollution norms. Since the baffled reactors work very well, there is complete digestion of solids and usually there are no emptying or cleaning requirements unlike a septic tank. The quality of treated wastewater that emerges into the polishing pond is good enough for landscape applications. The reed bed system in the filter part can be a very good landscape feature with plants like canna offering a colourful and verdant look.

The DEWATS approach reports a 80 to 85 per cent reduction in BOD and COD, a 80 per cent reduction in phosphates and a 60 per cent reduction in ammonia from the input wastewater.

The Bremen Overseas Research Development Association (BORDA) ( www.borda.de) has been at the forefront of DEWATS research and outreach globally and has installed thousands of systems. More information is available on the website www.bord-sa.org where the Centre for Dewats Dissemination (CDD) is working.

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