HOUSING lower- and middle-class blacks,certain South African townships areseriously threatened by contaminationcaused by human wastes. With nosewage disposal system, the residents ofthese poor localities use buckets toexcrete and once these are full to thebrim, the waste is either dumped intostreams or on the outskirts of the townships (ScientificAmericah, Vol 273, No'5).
The dumping of these wastes isproving to be a major threat to the environment, as not only are the streamsaffected by it but even groundwatersources lying just four metres below thesurface are.being polluted. But help ison the way. Peter D Rose of the Rhodes,University in SouthAfrica is using analgae-based system to solve the crisis. Apilot plant constructed nearby willreceive the waste emitted by 500-1,000people, through a 1,00,000 ha area ofponds and channels filled withspirulina. The single-celled plant thriving on salty, nutrient-rich sewage offerssolace to millions of helpless South.Ilicans. When exposed to sunlight,these plants seek higher dissolved oxygen levels and ingest most of the waste,and the remaining heavy metals andinorganic detritus settle at the bottom ofthe waterbodies.
Sewage processing by algae, an age-old method, is now being made moreeffective by advanced technologies. Inthe past 10 years researchers have concentrated on cultivating algal specieswhich can do even bitter than the activated-sludge process practised by industrialised nations. The algal pondsdo not require the equipment andpower needed to run the conventionalactivated-sludge ponds. This reducesthe building and operation costs byabout a half. These plants do not consume much water, which is an important innovation for and South Africa.The resultant sludge produced is alsolesser in quantity, making it easier totruck it down to landfill sites. Not onlythat, but most of the sludge is usuallytonnes of dead algae, which once dried,makes good fertiliser and,fish-foodadditive. Another *advantage of algalponds is that they do not stink, as thealgae only produce a lot of oxygen andnot other rotten smelling gases.
For Rose, the technology serves adual purpose. It holds the potential forimproving community sanitation and ata low cost, making it attractive to theneeds of developing countries., "One ofthe future benefits of the process is thatonce you have this algal biomass, youmight be able to engineer it to produce by-products that are more valuable thananimal feeds," he says. His teamrecently studied another algae,Dunaliella salina, which when exposedto excessive salt or heat, produces largeamounts of beta-carotene (a nutrientused by the body to make vitamin A).
Rose has also demonstrated the usefulness of the system in treating industrial waste, from tanneries. Tannerywaste includes effluents like sulphides,ammonia and heavy metals, which notonly give off bad odour but are alsoamong the most dangerous pollutantsto be emitted by any industry. Rose triedout the spirulina treatment on thiswaste, when he noticed that the plantflourished in a tannery's evaporationpond. The treatment systems tried outin Transvaal, Namibia and Cape Towntanneries show promise, as they havebeen successful in squelching odour andreclaiming water lost through evaporation. With the expected expansion inthe tanning industry in South Africa,the algal-pond system is expected to be amajor boon to the country.
Says Rose, "Rapid industrialisationin the Third World often happens at theexpense of the environment, becausethe costs of First World technologies toremedy the situation cannot be bornesimultaneously. To come up with a low-cost solution that results in somethingnot just safe but useful - well, that isthe first prize in biotechnology."