7. Directive 91/271/CEE • It concerns the collection, treatment and discharge of urban and industrial waste water; • The aim of the Directive is to protect the environment from the adverse effects of the waste water discharges.
8. BASIC CONCEPTS • urban waste water : domestic waste water or the mixture of the previous with industrial waste water and/or run-off rain water; • domestic waste water : waste water from residential settlements and services, which originates predominantly from the human metabolism and from household activities; • industrial waste water: any waste water which is discharged from premises used for carrying on any trade or industry, other than domestic waste water and run-off rain water;
14. Based on design for future requirements at year 2010 : Station of Processed Sewages 356 l/sec Irrigation: Design Anticipated Demand 324 l/sec Irrigation: Max. Anticipated Demand 31,100 m 3 /day Design Flow to Works 25,900 m 3 /day ( 3 * DWF) Peak Flow to Works 8,500 m 3 /day (DWF) Ave. Flow to Works 46,340 Design Population
15. IN GENERAL Sewage is pumped from Larnaca into the inlet of a pre-mixing chamber at the entrance of the works. Also pumped into the chamber are returned activated sludge from the final settlement tanks, miscellaneous supernatant liquors and sewage from the administration building.
16. PRIMARY TREATMENT From the mixing chamber the sewage passes to the inlet works, comprising screens and a grit removal plant. These two items of plant are contained within a building which is force – ventilated through an odor control unit to minimize smell problems.
17. SECONDARY TREATMENT The secondary treatment comprises of two parallel oxidation ditches, each containing a pair of horizontal rotors, followed by two final settlement tanks (FSTs) where the water is separated from the sludge and sent to the Storage Lagoons (capacity of 1,000,000 m 3 ).
18. TERTIARY TREATMENT Filtration is provided by pumping the water into Rapid Gravity Sand Filters from where it passes to a Chlorine Contact Tank in which it is given a controlled dose of chlorine from the chlorinators. The water is then available for irrigation purposes via a network of pipes. During summer approximately 17000 m 3 of water, at 10 bar pressure, are provided for irrigation daily.
19. SLUDGE Activated sludge in the FSTs is drawn off and a set percentage is pumped back to the pre-mixing chamber. Surplus sludge is thickened ( 2,5 % dry solids ) and then treated in aerobic digesters for 15 days before being dried in open drying beds.
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21. Station of Processed Sewages Post - Tertiary Post Secondary Incoming 400 kg/ day (47 mg/ l) 3240 kg/ day (380 mg/ l) 2550 kg/ day (300 mg/ l) 3 mg/ l 30 mg/ l 20 mg/ l 3 mg/ l NH 3 10 mg/ l SS 10 mg/ l BOD
24. Beds of Desiccation Sludge Drying Beds The sludge drying beds were provided to enable moisture content of the digested sludge to be reduced by the drying action of the wind and sun. Once the sludge reached an acceptable dryness it was removed manually from the beds by shoveling into a skip. Dehydration of Biolaspis
25. Dehydration of activated sludge The results of the method mentioned previously regarding the reduction of the moisture content, were not satisfactory especially during winter time.
26. Dehydration of activated sludge To be precise, although during the summer months 11 days were needed for the sludge to de-water, for the remaining months the sludge did not dry and therefore could not be removed.
27. Dehydration of activated sludge As a result of not removing the sludge, the MLSS values at the Plant rose from 2500 to 16500 The constant deposit of sludge at the Plant required a greater consumption of electric energy.
28. Dehydration of activated sludge With the installation of the Belt Press in October 2003, with a capacity of 22,1 m 3 /h, the problem gradually started to and it is estimated that by the end of 2006 the Μ LSS values will be within limits.
29. Dehydration of activated sludge Belt filter Press Unit From the digester the raw sludge is firstly mixed with a polymer solution before it enters the pre-dewatering step.
30. = The sludge pre-dewatering is carried out by means of a pre-dewatering drum where the excess water is drained away through the drum outer filtering cloth. The sludge discharged by the pre-watering drum is distributed over the cloth. In the first phase the sludge dewaters by gravity.
31. The the cake. The compressed cake falls down from the belts onto a conveyor which transfers the sludge into a skip. The skip is towel away sludge is then dewatered on the belt press . The clothes while running, are getting near each other wedge-wise, and are compressing gradually the sludge. The clothes winding up on the cylinders compress strongly the sludge cake, thus causing the dewatering of by a tractor.
32. Filtrate and wash water from the belt press are removed by a tray and pipe work situated beneath the belt press unit. The filtrate is directed to the existing Works Washout Pump Sump for returning to the inlet works via existing pumps. The connection for this pipe is made at the drain from the rapid gravity sand filters.
33. The dried sludge is conveyed to a trailer for removal by tractor and is situated in the existing drying beds.
34. The sludge is situated in the drying beds. The produced sludge is stored in the dry beds until transported to the fields for agricultural use. The transportation is done twice a year. At the end of May (after harvest) and at the end of September (before ploughing).
36. Introduction: For the use of sludge as an enhancer, there were reactions initially from farmers who were unsure of its use as a fertilizer for their fields. For this reason, specialists from LSDB and from the Agricultural Department were sent to several villages and farmers’ meetings in order to explain the importance of the sludge’s use. Use of activated sludge
37. Use of activated sludge Selection of fields according to the chemical characteristics of the soil. For this purpose samples are taken from several spots from each field and the results of chemical analysis indicate whether the fields are appropriate for adding sludge. The approval is obtained from the farmer, the local authorities, the Environmental Services and the Agricultural Department.
38. Use of activated sludge The table shows the sludge analyses of heavy metals in December 2005. 0,81 40 (Cd) Cadmium ( mg/kg ) LSDB PLANT LIMITS PARAMETER (Hg) (Zn) (Pb) (Ni) (Cu) 1,14 393 11,8 12,8 104 25 4000 1200 400 1750 Copper Nickel Lead Zinc Mercury
39. Use of activated sludge Application rate: Limit values for amounts of metals which may be added annually to soil. LIMITS ( kg/ εκτάριο/έτος) PARAMETERS (Hg) (Zn) (Pb) (Ni) (Cu) (Cd) 0,1 3 15 3 12 0,15 Cadmium Copper Nickel Lead Zinc Mercury
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45. Monitoring and control According to the terms and conditions for use on land the soil of the fields is analyzed prior to sludge spreading and afterwards every six months.
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48. THANK YOU FOR YOUR ATTENTION SPECIAL THANKS TO LARNACA SEWERAGE BOARD
