Surface Disposal (Liquids)

If there is no other more productive reuse intention the final effluents from sanitation systems that underwent a proper treatment (see also horizontal, vertical flow and free-surface flow constructed wetlands, waste stabilisation ponds, aerated ponds or rotating biological contactors) can be discharged directly into receiving water bodies such as creeks, rivers, lakes etc.

This allows recharging these surface water bodies, linked groundwater resources (see also surface groundwater recharge and sub-surface groundwater recharge) and thus contributes to the overall integrated management of the water resources (see also the water cycle and IWRM).

The use of the surface water body, whether it is for industry, recreation, spawning habitat, etc., will influence the quality and quantity of treated wastewater that can be introduced without deleterious effects. 

Alternatively, water can be discharged into aquifers. Artificial groundwater recharge is the planned infiltration of effluents from sanitation systems (e.g. wastewater stabilisation ponds, surface, horizontal flow or vertical flow constructed wetlands), stormwater or surface runoff into the aquifer in order to increase the natural replenishment of groundwater resources. Artificial surface and subsurface groundwater recharge refer to different groundwater recharge techniques that release effluent from above or below the ground into the groundwater via soil percolation. Artificial recharge can be of two types, mainly surface ground water recharge or subsurface ground water recharge. Groundwater recharge is increasing in popularity as groundwater resources deplete and as saltwater intrusion becomes a greater threat to coastal communities. It is also useful in areas where soil salinisation or water scarcity in general exist. Artificial recharge has also been used for many other beneficial purposes. These include additional treatment (through soil filtration, see also soil aquifer treament) and conservation or disposal of treated wastewater or floodwaters, crop development, stream flow augmentation, as well as storage of water to reduce pumping and piping costs as well as temporary regulation of groundwater abstraction (ASANO 1985, OAKSFORD 1985, UNEP 1998). Soil aquifer treatment can moreover increase water quality through the removal of suspended solids via soil filtration or through the dilution with naturally occurring groundwater (ASANO 1985). Although the soil is known to act as a filter for a variety of contaminants, groundwater recharge should not be viewed as a stand-alone treatment method. Once an aquifer is contaminated, it is next to impossible to reclaim it.

It is necessary to ensure that the assimilation capacity of the receiving water body is not exceeded, i.e. that the receiving surface or groundwater body can accept the quantity of nutrients without being overloaded (see also water pollution and pathogens and contaminants). To avoid chemical reactions that would reduce aquifer porosity and recharge capacity, the recharge water must also be chemically compatible with the naturally occurring groundwater and the aquifer material that it flows through. Parameters such as turbidity, temperature, suspended solids, BOD, nitrogen and phosphorus (among others) should be carefully controlled and monitored before releasing any water into a natural body. Local authorities should be consulted to determine the discharge limits for the relevant parameters as they can widely vary. For especially sensitive areas, a post-treatment technology (e.g., chlorination, see also post treatment methods) may be required to meet microbiological limits.

Polluted wastewater should be treated before surface/subsurface groundwater recharge. The quality of water extracted from a recharged aquifer is a function of the quality of the wastewater introduced, the method of recharge, the characteristics of the aquifer, the residence time, the amount of blending with other waters and the history of the system. Careful analysis of these factors should precede any recharge project. See also surface groundwater recharge and subsurface groundwater recharge to read more on typical methods how to recharge groundwater.

Generally, cations (Mg2+, K+, NH4+) and organic matter will be retained within a solid matrix, while other contaminants (such as nitrates) will remain in the water. There are numerous models for the remediation potential of contaminants and microorganisms, but predicting downstream or extracted water quality for a large suite of parameters is rarely feasible. Therefore, potable and non-potable water sources should be clearly identified, the most important parameters modelled and a risk assessment completed.

Regular monitoring and sampling is important to ensure compliance with regulations and to ensure public health requirements (see also water pollution and pathogens and contaminants). Depending on the recharge method, some mechanical maintenance may be required. In order to guarantee smooth operation and prevent any risk of pollution of clean aquifer, a thorough and detailed hydro geological study should be conducted before selecting the site and the method od recharge. In particular, the following basic factors should be considered (UNEP 1998):

• Location of geologic and hydraulic boundaries
• Depth of the aquifer and transmissivity of the overlying material
• Lithology
• Storage capacity
• Porosity
• Hydraulic conductivity and natural in- and outflow of water to/from the aquifer
• Availability of land, surrounding land use and topography
• Economic and legal aspects concerning the recharge
• Degree of public acceptance