Survey on Treatment of Wastewater in Wastewater Treatment Plants

Methodological Note on the Survey on Treatment of Wastewater in Wastewater Treatment Plants

The Survey on Treatment of Wastewater in Wastewater Treatment Plants was conducted by the Statistical Service of Cyprus in cooperation with the
Water Development Department of the Ministry of Agriculture, Natural Resources and Environment. The survey was harmonized with the definitions and methodology that were set by Eurostat (the Statistical Office of the European Communities) and was conducted in accordance with the requirements of the relevant Eurostat/OECD questionnaire.
The survey covered the years 2004 and 2005. Two questionnaires were designed for the collection of the data. The one was addressed to the
Sewerage Boards which operate and mmaintain wastewater treatment plants and the other to non-public wastewater treatment plants, such as in industries, hotels and other establishments.
In order to set up a complete and updated inventory of wastewater treatment plants in operation, information was extracted from records of the Water Development Department, the Department of Town Planning and Housing and the Environment Service (which is the authority responsible
for granting permits regarding the operation of wastewater treatment plants), as well as from the enterprises which construct and maintain such plants.
The information requested from the Sewerage Boards and the other wastewater treatment plants included the year the plant started its operation, the resident population served by the plant, the level of treatment of the wastewater the plant achieves and the capacity of the
plant. In addition, data regarding the quantities of wastewater treated in the plant in the years 2004 and 2005, the chemical analysis regarding the quality of the wastewater, such as the BOD5, COD, Suspended Solids, Total Nitrogen and Phosphorus, the population equivalent and the production and disposal of sewage sludge were required.
The survey was partly financed by the European Commission through funds from the Transition Facility 2004 for the ten new member-states.


Definitions used
Resident population: The average over a year of the number of persons belonging to the permanent population living in a territory (i.e. tourists and visitors are not taken into account).
Population equivalent: The organic biodegradable load having a five-day biochemical oxygen demand (BOD5) of 60g of oxygen per day.
for which it was used or in the pursuit of which it was produced because
of its quality, quantity or time of occurrence. Cooling water is not considered as wastewater. Wastewater originates from two sources, domestic and industrial. Domestic wastewater is wastewater resulting from residential settlements and services which originates predominantly from the human metabolism and from household activities. Industrial wastewater is water discharged after being used in, or produced by, industrial production processes and which is of no further immediate value to these
processes.
Wastewater collecting system: It is a system of conduits which collects and conducts wastewater. Collecting systems are often operated by public authorities or semi-public organisations.


BOD capacity: The total quantity of oxygen-demanding material that a wastewater treatment plant is designed for which can be treated daily with a certain efficiency.

Wastewater treatment: Process to render wastewater fit to meet applicable environmental standards or other quality norms for recycling or reuse. Different types of treatment exist. For purposes of calculating the total amount of treated wastewater, volumes and loads reported are shown only under the highest type of treatment to which it was subjected.
Primary treatment: Treatment of wastewater by a physical and/or chemical process involving settlement of suspended solids, or other process in
which the BOD5 of the incoming wastewater is reduced by at least 20% before discharge and the total suspended solids of the incoming waste water are reduced by at least 50%.
Secondary treatment: Treatment of wastewater by a process generally involving biological treatment with a secondary settlement or other process, resulting in a BOD removal of at least 70% and a COD removal of at least 75%.

Further treatment: Treatment (additional to secondary treatment) of nitrogen and/or phosphorous and/or any other pollutant affecting the quality or a specific use of water: microbiological pollution, colour etc. The following minimum treatment efficiencies define a further treatment: organic pollution removal of at least 95% for BOD and 85% for COD, and at least one of the following: · nitrogen removal of at least 70%
· phosphorus removal of at least 80% · filtration · microbiological removal achieving a faecal coliform density less then 1000 in 100 ml
Nitrogen removal: Facility of a wastewater treatment plant to bring the efficiency for nitrogen elimination to a high level. This can be done by creating special process conditions to stimulate nitrification and
denitrification.
Phosphorus removal: Facility of a wastewater treatment plant to bring the efficiency for the elimination of phosphorous to a higher level. This can be done using chemical and/or biological processes.
Sewage sludge: The accumulated settled solids separated from various types of water either moist or mixed with a liquid component as a result of natural or artificial processes.


Last updated: 24/07/2007