The arrangements at the Tunweni Sorghum Brewery, Tsumeb, Namibia are such that wastewater is utilised in the polyculture of locally available riverine fish species in 3000 m2 large, 3 meters deep earthen ponds. Before reaching the fishponds the wastewater passes through a series of bio-system processes such as mushroom and earthworm beds, a pig sty, anaerobic and aerobic digesters and algae ponds. Spent grains from the brewery process are rich in fibers and protein and they are used as substitute for flour in bread. When mixed with other fibers such as rice straw, they are also used as a valuable ingredient in the substrate for the growing of mushrooms.
Description of the Process
The Tunweni Sorghum Brewery, located 16 kilometres north of Tsumeb, consists of a brewery house, a mushroom and vermiculture house, an animal house, settling/filtering/sump tanks, a bio-digester, shallow algae ponds, deep fish ponds and irrigated land adjacent to a 600ha irrigated area with orange and mango trees. The brewery house is situated on slightly sloping ground, with the result that gravity supports the flow of waste materials. The brewery operates four days a week, Monday to Thursday, with Friday being devoted to washing and disinfecting. The Tunweni Sorghum Brewery produces sorghum beer (5% alcohol) and the makeu — a non-alcoholic beverage. Its by-products are fluid waste (wash water and unsold beer) and solid waste (spent grain). Unsold beer is returned to the brewery and is added into the wastewater stream. Spent grain is separated from the fluid by filtering, leaving some active yeast on the spent grain and in the beer. The spent grain is used for feeding animals, as a mushroom-growing substrate, in vermiculture and in the distillation of technical alcohol. At present the spent grain provides 50% of the animal (currently pigs) feed; results from trials show that pigs lose weight when fed on spent grain alone and that spent grain only comprises about 6% fibre and about 65% moisture content. A 50% ratio of spent grain and chopped grass is soaked with water to provide substrate for mushroom growing. Sterile conditions are required for the inoculation of the mushrooms. The mushroom Mycelia digest the cellulose of the spent grain and turn it into high proteinous food consumable by earth worms; the mushroom bulks after fruiting are subsequently used in culture. In experimental trials of the vermiculture the earthworms died. Due to the high yeast content thereon, fermentation continues on the spent grain and the alcohol kills the earthworms and may intoxicate livestock. The solution to the problem may be the introduction of distillation to recover technical alcohol from the spent grain. Currently four to five tonnes of spent grain are produced per week. The waste water from the brewery, comprising about 12m³ of wash and disinfectants per week, plus the returned beer, flow into settling/filtering/sump tanks where excess solids settle and are removed. As a result, filters are prevented from clogging and the settlables removed are used for feeding animals. The fluid flows into the anaerobic biodigester, which operates at temperatures of between 35–40°C and a retention time of 45 days, for fermentation. Sewage from the office building flows directly into the biodigester. Manure from the animal shed is also washed into the bio-digester where it mixes with the rest of the waste materials. At full operation approximately 200 litres of fluid are estimated to flow into the bio-digester every day. Methane gas is produced from the bio-digester. Workers on site use this for cooking meals. At Songhai in Benin, West Africa, the gas is compressed and stored in tanks for use in producing energy for lighting, heating, propulsion, and other kinds of power generation. Runoff from the digester flows into the shallow algae basins. The algae, dominated by Chlorella sp., currently contains about 50% wind-blown sand from the surroundings and is not fit for direct animal consumption. The algae are harvested and added to the bio-digester. Water from the algae beds is used to irrigate the lawn and trees and in canal irrigation of crops such as maize, mohangu, melons and mangoes. The rest of the runoff from the algae beds flows into the fish ponds.
A traditional brewery of today, that brews beer according to the German purity standards, produces beer, but also produces organic waste streams and lost energy. This waste from the brewery is organic material which means that its polluting effect could be seen as minimal. However, given the quantity of water needed for the large volumes of beer produced by today's breweries (up to more than 20 liters of water per liter of brewed beer), this organic waste is a problem. It is also a waste considering the amount of nutrients and protein used from the grains in the beer-brewing process. A small percentage of the nutrients are used, and the protein is left untouched in the spent grains after the process. One usage for the spent grains that is occasionally explored is that of animal feed. This is not an optimal use, though, as the spent grains are tough for the animals to digest. The result is indigestion and added amounts of methane gas emitted into the atmosphere by the animals.
Factors that contributed to the success of the project
The advantage of growing mushrooms on the spent grains is that mushrooms will make the spent grains more digestible to livestock and will also increase the protein content. This will thus increase growth of animals and quality of meat.