44 ENVIRONMENT AND ENERGY
Many large cities in developed and transitioning economies have extensive sewerage systems , some of which are still functioning effectively some 100 years after construction . or pervious surfaces capture rainwater before it runs onto polluted pavements and streets . These solutions can alleviate peak flows , minimise the risks of urban floods and pollution , and reduce the need for investments in additional hard infrastructure and treatment facilities . They can attract private investments , encouraging property and land developers to invest in new buildings equipped with localised drainage systems .
This may require changes in local by-laws , as local regulations will , to a great extent , dictate the final choice . On the other hand , decentralised stormwater drainage only offers a solution for temporary retention , as the water will ultimately need to be transported to sewer systems . In some cases , the maintenance costs will be higher , but decentralised systems help to attain benefits like improved human wellbeing , absorption of air pollution and moisture retention , thus lowering ambient temperature and attenuating the urban heat island affect , ultimately contributing to the greening of cities .
Decentralised systems can also be used for the treatment of runoff from highways . Experience accumulates with the implementation and exploitation of decentralised sanitation and urban drainage . Nonetheless , some barriers have to be overcome , such as social perceptions and difficulties associated with retrofitting . situation or by other factors like global warming , water scarcity , environmental quality issues and / or land use planning . In the rapidly urbanising centres worldwide , the prevention of the discharging of carbonaceous material was the priority in order to protect receiving waters being starved of oxygen .
The oxygen demand was ‘ satisfied ’ by using large amounts of energy to encourage the growth of microbial biomass ( sludge ), which was separated from the system and used in agriculture or dumped at sea . Later developments saw extended aeration systems to reduce the final amount of biomass for disposal , as this was responsible for a large proportion of the treatment costs . During the oil crisis in the
An additional challenge is the need to manage wastewater at different scales ( from buildings to the municipal level , to even larger levels ). These barriers can be overcome by a combination of information campaigns , a whole-of-government approach to urban water management ( including policies , laws and regulation ), business models for water utilities and land development that factor in externalities related to wastewater management , and a long-term vision of the challenges in the water sector and the opportunities for urban development .
EVOLUTION OF TREATMENT TECHNOLOGIES Significant advances have been made in treatment technologies , since the original development of aerated systems ( e . g . activated sludge and trickling filters ) during the 1920s . The selection of treatment systems has been driven by the prevailing economic
August 2018 Volume 24 I Number 6 www . plumbingafrica . co . za