Swim, sprinkle and burn

Waste water treatment will bring more than just crystal waters. Clean seas and more greenery could go some way toward turning Malta and Gozo into the island paradise we all would like to live in.

The technology for producing clear water, from waste water, that is well within the safety limits for bathing, almost drinking quality, and agriculture is with us today.

As it stands we currently use up large amounts of electricity to get half our fresh water from the sea and drain our aquifers dry for the other half. At the same time we are tainting our waters, pouring un-treated sewage into the very same seas in which we swim and fish.

Our island faces two big problems which come to a head every summer - the amount of sewage we produce and not enough water to meet basic agricultural needs.

Last July Mellieha farmers suffered crop loss when boreholes ran dry as agriculture competed with the hotel industry for every last drop of ground water.

Chief executive officer Anthony Rizzo points out that private extraction is twice what the Water Services Corporation (WSC) pumps up for blending with reverse osmosis water.

We produce 34 million cubic metres of water annually through RO and pumping up of ground water. Much of this ends up in the 30 million cubic metres of sewage we discharge into the drains.

Only ten per cent is partially treated at the Sant Antnin plant. Primary treatment is now an EU requisite. Desalinated water for use once only is costing us a lot of energy and chemicals to produce.

Membrane bioreactor technology

Senior government ministries were contacted this month by the Aquator Group's UK division with a bid for waste water that is as simple as it is small scale and suited to our congested island.

The company has developed a system first applied in Japan using membrane bioreactor (MBR) technology. A quarter of the size of conventional treatment plants, the MBR technology produces second class water of a very high quality with potential commercial reuse value.

Water resulting from MBR treatment does not have to be pumped out to sea before it can be released.

Problems caused by the continual vandalism on long outfall pipes by irresponsible fishermen become redundant. The effluent is clean, clear and safe enough to mix in directly with the waters in any bathing bay.

At a seminar to introduce this type of waste water treatment it was suggested that Malta could recharge its aquifers, a proposal which is not exactly new. The WSC has always treated the subject with extreme caution whenever it has been mentioned in the past.

We cannot afford to make a mistake which would put half our water supply out of operation. Anthony Rizzo is very conscious of the bearing the state of our aquifer has on national health.

On the other hand, like throwing away glass bottles and other recyclables, we could be wasting a valuable resource when we pour our waste water untreated into the sea.

The effluent resulting from MBR is claimed to be cleaner than Maltese coastal waters. It meets the EU Bathing Water directive for bacteria and virus removal before it has been put in the sea.

In theory (although the directive on bathing water quality is not applicable to swimming pools) one could safely fill a swimming pool with the treated effluent and swim in it.

Bacteria are not all bad. While responsible for much human misery they are also miraculously capable of digesting toxins that would normally linger on and poison us.

Research is ongoing in the field of employing bacteria to clean up sewage, oil pollution and even attack the dreaded dioxins found at mismanaged dumpsites.

MBR showcases

Wessex Water, the water authority for the Bath area in the UK, runs one of 900 MBR waste water treatment plants worldwide at the coastal town of Swanage.

The plant sits unobtrusively at the edge of a picturesque bay in an environmentally sensitive area serving 23,000 people. The treated effluent is of such high quality that it can be discharged directly into the sea with no ill effects on the nearby bathing beach.

Picnic Bay's MBR plant on an island off the coast of Queensland has been designed to meet possibly the most stringent consent ever placed on a municipal waste water plant for its size.

The Australian plant which can serve up to 8,000 people came into commission last year at the world's largest coral reef a World Heritage Site.

Environment agencies want to know the test results of sample monitoring. In this respect MBR plants are not complicated to run requiring only basic infrequent checks. Weekly monitoring by the environment agency may be relaxed when consistently good readings are found.

By rule of thumb if the water is clear it is likely to pass most other tests. Reporting is made easy compared to systems using UV disinfection when power failures could mean fines for the water company for non-compliance. Membrane reactors are less susceptible to power cuts being largely a bacteriological process aided by gravity.

Effluent feed for RO plants

There are at least three things we could do with high quality effluent from waste water: Re-use of treated effluent on a large scale is quite feasible for agriculture and industry. Water would fetch a better price and offer a better guarantee on quality.

Used as a pre-treatment for desalination MBR effluent would reduce the operating costs of RO plants. It is claimed that polishing the treated water through RO plants would make them 80 per cent more efficient than using sea water.

The third and most controversial use for effluent would be to replenish our water table and impede intrusion of salt water into the aquifer. At present extraction is greater than what is going back in the ground by rainfall.

Special rules for artificial recharges of ground water intended for public water supplies are listed under the European directive on the protection of ground water against pollution.

Presently faecal concentrations in second class water produced at Sant Antnin are considerably higher than MBR. Retro-fitting Sant Antnin with bioreactor membranes could triple the plant's present through flow and reduce chemicals needed for cleaning.

Ten to 12 different chemicals are currently used at RO plants in Pembroke, Cirkewwa and Ghar Lapsi. Membrane technology would reduce the need for chemicals from eight kilos to a quarter kilo for the same amount of water treated.

Applications for industry

Malta's pig and cattle farms pose environmental challenges over the nitrate load they add to the sewerage system. Dairy waste also carries a significant phosphorous load. Alum can be added to reduce phosphorous and removal of nitrates can be built into the MBR process by adding denitrification.

The food and beverage industry, breweries, textiles and the shipping industry could make use of MBR plants which can be retro-fitted to existing plants.

They are particularly suitable for cruise ships travelling the scenic waters of specially protected areas such as the Arctic or the Florida Keys.

Ideally irrigation of agricultural land with second class water from MBR plants can be best made use of if factories and farms are located near outfalls.

Treatment at source is recommended for industries. If industrial waste water is pumped across the island to the treatment plant there is a risk that leaky pipes could allow some of it to seep into the ground contaminating the aquifer. Treating waste water on site would also reduce the hydraulic load on the current sewerage infrastructure.

Noise and smells do not seem to be a problem with MBR plants. Covered tanks mean that odour emissions are undetectable. One plant is built very close to an outdoor theatre with no apparent ill effects.

Irrigation water from MBR effluent is sprayed into the air through sprinkler systems in areas used by the public. It is found to be well below WHO guidelines on reuse of waste water.

Concerns over the extent to which this system could handle a mixture of municipal sewage waste and industrial effluent were expressed during the seminar.

The engineers explained that the advantage of MBR is complete retention of solids. Bacteria find mechanisms to deal with the more difficult components such as toxic heavy metals in the waste stream which are retained in the sludge.

Aquator's plants include systems for treatment of petrochemicals and pharmaceutical waste, both dedicated and combined.

Sludge as fuel?

Sludge formed during the treatment process can be turned into an effective fertiliser. A secondary function of the membranes is to thicken sludge to a concentration of up to 50,000 grams per litre, nearly half the biomass produced by conventional treatment.

Wessex Water runs a thermal drying plant turning the sludge into nutrient rich granules. The bio-drier enabled WW to stop disposing of sludge at sea six years ahead of a legal deadline.

The EU's Urban Waste Water Treatment Directive meant that disposal at sea had to end by 1998.

Another EU directive, which came into force that year prevents farmers from using raw sludge on food crops. (We have been known to irrigate our crops with an unacceptable quality of water taken from sewage suitable only for cattle feed grasses and not vegetables for human consumption.)

The Directive has been quite successful in preventing crop contamination by pathogens caused by partially treated sludge on agricultural soils.

Why incinerate sludge when it can be a useful resource for the building industry? A government consultant has asked. The Department of Agriculture has even considered converting arable fields to forage to provide a sink for waste sludge rather than burning it.

The quality of milk would be improved if animals were fed fresh fodder instead of dried feed. Fields of grain would help prevent ground water pollution in Malta while providing an alternative to the incineration of sewage sludge.

Environmentalists might not agree with a monoculture solution unless a meadow ecosystem can be encouraged. Arguments against this idea hold that fertilising farmland is done on a seasonal basis and storage would only take up more valuable land.

So waste water treatment and the sludge left behind may indeed steer us toward recovering energy from biowaste plants. Heavy metal levels are still a concern.