Natural coagulants - a sustainable approac

Geoff K. Folkard (7219316)

John P. Sutherland (7219313)

Reya S. Al-Khalili (7223795)

English

Loughborough University Institutional Repository

G   WATER RESOURCES AND WATER SUPPLY: FOLKARD, SUTHERLAND and AL-KHALILI26321st WEDC Conference Kampala, Uganda, 1995Natural coagulants — a sustainable approachGeoff Folkard, John Sutherland and Reya Al-Khalili, UKSUSTAINABILITY OF WATER AND SANITATION SYSTEMSTHE M. OLEIFERA TREE is a native of Northern India whichnow grows widely throughout the tropics. English ver-nacular names include ‘drumstick’ (shape of the pods)and ‘horseradish’ (taste of the roots). It may be propa-gated from seeds or cuttings, even in poor soils, requir-ing minimal horticultural attention and is able to survivelong periods of drought. It grows rapidly - growth of upto 4 metres in height, flowering and fruiting were allobserved within one year during trials near Nsanje,Southern Malawi. Extended and multiple harvests in asingle year are evident in many parts of the world. Themany products and numerous uses of the tree are given:Vegetable• Green pods, leaves, flowers and roasted seeds arehighly nutritious.Oil• Seeds contain 40% vegetable oil by weight - may beused for cooking, soap manufacture, cosmetics baseand as a lamp fuel.Coagulant• Seeds used traditionally for ‘household treatment’ inthe Sudan and Kenya.• Successfully used at pilot and full scale water treat-ment works in Malawi.• Presscake remaining after oil extraction effective as acoagulant - bench scale testing.• Potential for use as an aid to primary sedimentationin wastewater treatment - bench scale testing.Other uses• All parts of the plant are used in a variety of tradi-tional medicines.• Presscake as a soil conditioner/fertiliser and poten-tially as an animal/poultry feed supplement.• Green leaves as a fertiliser - mulch.• Powdered seed used in ointment to treat commonbacterial skin infections.• Grown as live fences and windbreaks.• Fuelwood source following coppicing.• Agroforestry within an intercropping system - alsoproviding semi-shade.• Wood pulp for paper making industry.• Planted for specific protective and soil meliorationfunctions.• Planted as an attractive ornamental tree.M. oleifera is a multipurpose tree of enormous poten-tial. Multipurpose trees are cultivated and managed insuch a way that they foster sustainable land use withmore than one product and/or function. They are par-ticularly significant in agroforestry systems, performingspecific, protective and stabilising functions.Water treatmentRiver water drawn for human consumption and generalhousehold use can be highly turbid particularly in therainy season. River silt is churned into suspension andrun off from fields and other surfaces carries solid mate-rial, bacteria and other micro-organisms into the river. Itis of paramount importance to remove as much of thissuspended matter as possible prior to a disinfection stageand subsequent consumption. This can generally only beachieved by the addition of coagulants to the raw waterwithin a controlled treatment sequence. In many devel-oping countries proprietary chemical coagulants, suchas alum and synthetic polyelectrolytes are either notavailable locally or are imported using foreign exchange.A viable alternative is the use of crushed seed of M.oleifera as a natural coagulant. The seed pods are allowedto dry naturally on the tree prior to harvesting. The seedsare easily shelled, crushed and sieved using traditionaltechniques employed for the production of maize flour.The crushed seed powder, when mixed with water,yields water soluble proteins that possess a net positivecharge. Dosing solutions are generally prepared as 1-3%solutions. The solution acts as a natural cationicpolyelectrolyte during treatment. (Sutherland et al, 1990)River water treatment at pilot scaleIt is now regarded as axiomatic that both water andwastewater technology for developing countries must beno more complex than strictly necessary, be robust andcheap to install and maintain. A prototype treatmentworks was designed founded on this philosophy. Thepilot plant was constructed within the grounds of theThyolo Water Treatment Works, the works being con-trolled by the Ministry of Works and Supplies WaterDepartment of the Malawi Government. The system wassuccessfully commissioned during the 1992 rainy seasonwith the source river exhibiting turbidity levels in excessof 400 NTU throughout the study period. Solids removalwithin the plant was consistently above 90% following agravel bed flocculation stage and plain horizontal flowsedimentation. Subsequent rapid gravity sand filtrationG   WATER RESOURCES AND WATER SUPPLY: FOLKARD, SUTHERLAND and AL-KHALILI264The leaves have outstanding nutritional qualities -amongst the best of all the perennial tropical vegetables.The protein content is 27% and significant quantities ofcalcium, iron, phosphorous and vitamins A and C arealso present. A particular advantage to people nutrition-ally at risk is that leaves can be harvested during the dryseason when no other fresh vegetables are available.M. oleifera seed contains 40% by weight of oil. The fattyacid profile shows oleic acid at 73% confirming that theoil is similar to olive oil and thus of high quality and highmarket value. Laboratory tests at Leicester confirm thatthe presscake remaining after oil extraction still containsthe active constituents effecting coagulation. Coagulantmay be regarded as a by product of viable oil extraction.(Sutherland, 1993)Edible oils are an essential component of human nutri-tional requirements. In developing countries, the pro-duction and marketing of edible oils is usually domi-nated by a few large scale urban-based companies. Ruralsupplies of the finished product are erratic with in-creased prices due to additional transport costs.The Intermediate Technology Development Group(ITDG) in Zimbabwe have successfully introduced tech-nology appropriate for small scale decentralised ruralprocessing of edible oils. A recent evaluation of the 17 oilmills established to constitute this ITDG project con-cluded (Sunga and Whitby, 1995):• the oil mills are commercially viable returning anaverage of 51% on investment with profits of 21% onsales• a typical mill employs 10 permanent and 3 temporaryworkers• ready cash markets for oil seed crops had been cre-ated• lower cost oil of significantly higher quality is nowavailable in the rural areas.• alternative edible oil seeds such as soya, cotton seedand moringa should be investigated• the market for and sales of presscake are importantfor the overall viability and profitability of themills....new outlets are requiredConclusionsThe products of the Moringa oleifera tree are underex-ploited resources. Realisation of their potential will con-tribute towards sustainability in the rural areas, address-ing major issues of current concern:• water quality and health• food and nutrition• employment opportunities• income generationReferencesFolkard, G. K. & Sutherland, J. P. 1994, Moringa oleifera -a multipurpose tree, Footsteps, No.20, Sept. 1994, pp14-15.gave a final, treated water turbidity generally well below5 NTU. M. oleifera seed dose ranged from 75-250mg/1depending on the initial raw water turbidity. (Folkard etal,1993)River water treatment at full scaleIn February 1994, the main Thyolo works was operatedusing M. oleifera solution as coagulant. The works com-prise upflow contact clarifiers followed by rapid gravityfilters and chlorinator. The clarifiers are in a state ofdisrepair with the impeller drives and chemical feedpumps inoperative. Alum solution is introduced into theincoming flow of 60 cubic metres per hour by simplegravity feed. Comparable treatment performance withalum was achieved. Inlet turbidities of 270-380 NTUwere consistently reduced to below 4 NTU. This was thefirst time that M. oleifera had been successfully used as aprimary coagulant at such a scale with the treated waterentering supply. (Sutherland et al, 1994)M. oleifera seed for the full scale trials was purchasedfrom enthusiastic villagers in the Nsanje region. The treeis widely cultivated in this area, being highly prized as asource of fresh, green vegetable.Alum and soda ash (for final pH correction) for theThyolo works were imported from South Africa at anannual imported equivalent cost of £26,000 (March 1993).It was estimated that if the water utility established andmaintained a plantation of M. oleifera trees for oil produc-tion/ presscake coagulant, a net operating profit wouldbe achieved.Treatment of eutrophic waterTreatment studies have recently been conducted  atbench scale on a eutrophic lake water serving the maintreatment works to Harare, Zimbabwe. (Sutherland et al,1995) The impounded water contains much light organicmatter in suspension due to high algal growth  andexhibits relatively low turbidity throughout the year. Assuch, the water is problematic to treat consuming signifi-cant quantities of alum (as primary coagulant ) andactivated silica (as weighting agent). Alum floc carryover from the clarifiers causes “filter blinding” and thesludge from the clarifiers is voluminous , difficult todewater and presents pollution problems on dischargeto the receiving water. M.oleifera in combination withsodium bentonite as weighting agent produced a finalwater quality  equivalent to that produced using theconventional chemical coagulants. The sludge was sig-nificantly more compact  and represents a potentiallyuseful output as a soil conditioner/ fertiliser.M.oleifera as vegetable/oil sourceM.oleifera pods are an important commercial vegetablecrop throughout India. They are also exported freshunder refrigeration  and in cans to countries with size-able Indian communities.G   WATER RESOURCES AND WATER SUPPLY: FOLKARD, SUTHERLAND and AL-KHALILI265Folkard , G.K., Sutherland , J.P. & Grant, W.D. 1993,Natural coagulants at pilot scale ; In: Pickford , J. ed.Water, Environment and Management; Proc. 18thWEDC Conference, Kathmandu, Nepal, 30 Aug-3 Sept1992. Loughborough University  Press, pp 51-54.   .Jahn, S.A.A. 1988, Using Moringa seeds as a coagulant indeveloping countries, Journ. AWWA, 80, (6) pp 43-50.Morton, J.F. 1991,The horseradish tree, Moringapterygosperma - a boon to arid lands? Economic Botany,45, (3), pp 318-333.Ram, J. 1994, Moringa - a highly nutritious vegetablesource, TRIADES Technical Bulletin No.2,  Box E,Hakalau, Hawaii.Sunga, I. & Whitby, G. 1995, Decentralised edible oilmilling;  an evaluation report, May 1995, ITDG, Rugby,England.Sutherland, J. P. 1993, Oil and coagualnt extraction fromM. oleifera seed, Draft Report to the ODA, London,Sept. USA.

Natural coagulants - a sustainable approach

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Natural coagulants - a sustainable approach

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