Calculation of wastewater resources

The Wastewater resources module uses the concept of service zones.

A Service Zone is a zone that is served or which can be served by sanitary services. A Service Zone comprises various Demand Centers (DCs).

The service zones are described both in a GIS file and in a station-file WWTP_SERVICE_ZONE. The relation between Demand Centers and service zones is described in table SERVICE_ZONE_DEMAND_CENTERS.

The map below shows how settlements (Demand Centers) are spatially assigned via service zones to treatment plants.

It shows, however, also the specific problem for the city of Irbid. While the point-presentation of the city (i.e. the demand center) is assigned to WWPT "Irbid (Central)", the town extents (as shown by the polygon "Towns") fall also into the service zones of the existing WWTP "Wadi Al Arab" and the planned WWTP "Wadi Shalala (Irbid East)".

Therefore, in table SERVICE_ZONE_DEMAND_CENTERS, SETT_ID 140 (Irbid) appears on 3 records, each assigned to a different Service Zone. In order to avoid double-counting (or a tedious re-assessment of the coverage rate), the portion to contribution to that Service zone is given.


For historic years, wastewater resources have been directly monitored as outflow (effluents) from WWTPs.

However, for the future, wastewater resources need to be calculated as follows:

TPe = TPi * (100 - L)/100

with

TPi = RF * (Dm * Cov/100 + Dt ) * P/100 + Wi

and

Dm = municipal Demands (from table STP_MUNICIPAL)
Dt = tourist Demands (from table STP_TOURISTIC)
Wi = Wastewater generated from industries (field WASTEWATER in STP_INDUSTRY)
Industrial facilities are directly linked to WWTPs also according to the service zone, the earlier table WWTP_INDUSTRY_CONNECT is not longer used.

If the return factor RF is zero, it is assumed that the WWTP is not yet operational, and no wastewater flows from industries are taken!

TPi = Inflow to WWTP
TPe = Effluent from WWTP (= resource as result of this submodule)
Cov = Coverage
percentage of the population (not the number of houses) connected to the sanitary sewers to the total population living in the service zone
for historic years estimated values are available in table SERV_ZONE_POPU_COVERAGE. On the basis of this, future figures should be estimated. Typical values are between 30 and 80%. If population grows but the network keeps constant, coverage will decrease with time.
P = Portion of the population in % within a settlement to be served by a WWTP
stored in table SERVICE_ZONE_DEMAND_CENTERS and to no be modified by the user
Because of lack of data alternatives, this factor will also be applied to tourist demands.

Note: in order to comply with the approach ised in other reports, this factor is set as default=100.

RF = Return Factor
includes all losses like consumption in the houses (connected to the sewage system) and losses from (or inflows to) sewage systems
Very difficult to estimate even for historic data; a value of 0.7 may be realistic
L = Loss in WWTP due to infiltration and evaporation
typically between 5 and 25% depending on type of WWTP
can also be calculated for historic years out of ratio inflow_to / efffuent_from WWPTs