Decentralized Wastewater Treatment System

Decentralized wastewater management employs allavailable treatment and disposal technologies. The appropriatetechnologies in a measure that meets current needs and takesinto consideration future growth, are matched with thetreatment and disposal requirement that have been identified(Douglas, 1998).

Using decentralized wastewater treatment system savesmoney, protects the home owners investment, promotes betterwater shed management, offers an appropriate solution for lowdensity communities, provides suitable alternative for varyingsite conditions and furnishes effective solutions forecologically sensitive areas (USEPA, 1997).

Domestic WastewaterDomestic sewage is made up of human waste and sullage.

It’s main characteristics strongly depends on householdactivities e.g. cultural habits, living standard, demography,type of chemicals used e.t.c.

Sewage affects water bodies in three ways viz: contributesorganic matter and organic forms of nutrients; it addsintestinal bacteria (coliform) and other pathogens; it mayadd hard detergents of alkyl benzene sulphonate (ABS) base.

In the developing world, aside the human waste which isgiven special management attention, sullage is notconsidered as a threat; hence it is discharged withoutrecourse to any treatment option.

Fig 1a: Discharge of wastewater from bathroom in a low income setting of the developing world

Fig. 1b: Discharge of Wastewater from a Kitchen in a low income settings of the developing world

On-Site Water Treatment SystemsOn-site treatment of waste is a decentralized wastewater

treatment system that requires simple, reliable, low–energyconsuming and low-cost technologies that private owners with littleskills for operations can afford (Schudel and Boller; 1989).

Gravity percolation of wastewater through one kind or another ofpercolator material is a common on-site wastewater treatmenttechnology that fulfills these criteria. During transit through thepercolator, the wastewater is purified by physicochemical (filtration,adsorption) and biological (microbial degradation) process (Lens etal, 1994).

In the developed world, the use of on-site system has beenpromoted and it’s been accepted as a convention in the managementof waste from domestic source.

On- site methods on TrialAmongst the materials that has been introduced in the on-site

wastewater treatment of sewage in percolator systems are slag andground stones, sand, bamboo, straw, peat, sawdust, peat, compost,zeolites, wheat straw, newspaper, limestone, expanded clay, woodchips, wood fibers, mulch, glass, ash, pumice, bentonite, tire crumbs,expanded shale, oyster shells, soy meal hulls, clay minerals fortifiedwith gravel pebbles e.t.c.

Some of these materials have been proven to be an effectivematerial for the treatment of presettled domestic wastewater.

This approach was adjudged to have ‘‘green’’ implications because ofthe inclusion of recycled material as part of the material mixture,promoting treatment efficiency and cost effectiveness

On-Site Methods in Practice

In Finland, for instance, ditched peat lands are being used to treatliquid waste from small villages.

In response to Japan’s serious water pollution, the system namedShimanto-gawa system which uses only natural materials and nosynthetic chemical for the wastewater treatment of foul water outlets orpolluted streams before they enter larger water courses has beendeveloped.

On-site domestic wastewater treatment systems called Johkasoushave also been developed and become popular in Japan. These systemsare household-sized units with a capacity of 1–2 m3 day-1.

In Europe, a low-cost treatment technology known as theKikuth Reed Bed technology is being widely used for thetreatment of highly contaminated wastewater. The treatmentsystem is designed around soil-based plant and microbiologicalreed beds.

In China, a high performance, low-cost wastewater treatmenttechnology known as Eco-Pond has been established. The pondsystems have been used as a popular alternative treatmentmethod in remote and less affluent regions since the 1970’s.

Chosen On-Site System for Management of Domestic Wastewater

Protection of public Health: create an effective physical barrierbetween contaminated wastewater and user.

Protection of the Environment: prevent euthrophication and pollution.

Ensuring soil fertility: If wastewater is reused, short or long-termimpacts on soil should be prevented.

Socioculturally and economically acceptable: Adaptation to the socio-cultural and economic settings of the household or neighborhood

Simple and User friendly: systems should be manageable by the user.

Compliance with national and international regulations andstandards: Qualitative and quantitative effluent standard need to bemaintained.

Specifically, six areas of responsibility have been identified asessential to on-site system effectiveness (Ruiter, 1981): Planning(e.g. subdivision layout); Site evaluation (e.g. percolation test);Design (e.g. leachfield sizing); Installation (e.g. systemconstruction); Operation (e.g. loading); Maintenance (e.g.septage pumping).

Traditionally, the responsibility for the first four functions hasbeen assumed by local or regional health departments, whileoperation and maintenance have been left to the home owners.

Since homeowners attitude to the assumption of theseresponsibilities in a conscientious manner is apathetic, on-sitesystem have not always been viewed as a viable, permanentapproach to wastewater treatment and disposal.

On-Site System Management Scheme

Ward, (1984) opined that if professional operation andmanagement is provided, there is no reason why on-sitetechnology cannot be considered a long term, permanentwastewater treatment option, capable of being expanded as thecommunity grows.

Considering the challenges in the developing world the use ofoperation and maintenance professional may not be workablebecause of the communal lassitude towards such professionalsand the cost implication on the part of the homeowners

In order to get the homeowners involved in the operation andmaintenance of such facilities a reorientation on the need to adoptthe recommended procedure for sewage management and thedanger of poor management of this system is expedient.