TREATMENT OF PERCOLATE FROM DUMPING SITE

The percolate is the fouled liquid sewage that forms, in an anaerobic environment, in a dumping site producing methane, carbon dioxide, high boiling organics (COD surface active agents, oils, greases. etc), low boiling organics (free acids, etc), ammonia, anions (chlorides, sulfides, etc), cations (metals, sodium, etc), suspended and settling material.

Due to the large possibility of very large types of composition, as you can see from the side table, is compulsory to proceed with an analysis before of the elaboration of the offer, just to characterize the type and composition of the liquid.	pH	5,0 ÷ 8,8
	COD, mg/l	500 ÷ 30.000
	BOD5, mg/l	50 ÷ 17.000
	NTK, mg/l	20 ÷ 6.000
	Metals, mg/l	5 ÷ 500
	Chlorides, mg/l	800 ÷ 5.000
	Sulfides mg/l	600 ÷ 4000
	Nitrates, mg/l	50 ÷ 800

The treatment of a percolate from a dumping site can be briefly described as follows:

1. Extraction, accumulation and settling;

2. Pretreatment: pH correction and incondensable elimination;

3. Multi effects vacuum evaporation;

4. Finishing on osmotic membranes;

5. Treatment on activated carbon;

6. Stocking of the final treated liquid;

1) Extraction, accumulation and settling The meteoric waters that are percolating trough the material of a dumping site are collected, periodically, by a pumping station from the sump pits and stored in covered pools or storage tanks. This liquid accumulation allows the settling separation of the most of the suspended materials. From the liquid bottom a pumping station send the settled material again to the dumping site. A second pumping station feeds the pretreatment unit.

2) Pretreatment: pH correction and incondensable elimination The settled waters are submitted to a double treatment for the correction of its pH and the elimination of the incondensable. The pH correction permit to block efficiently the dissolved ammonia. The acidification process involves the developing of carbon dioxide that is producing the formation of foam. The emissions into the atmosphere from the incondensable eliminatoion process must be evaluated with a pilot plant, in order to caracterize the kind of emission and the subsequen abatement plant. The following multi effects evaporation unit is designed to minimize the energetic consumption of the second stage of the pretreatment.

3) Multi effects vacuum evaporation The liquid that feeds the evaporation unit is taken from the second stage of the pretreatment and is submitted to a vaccum distillation with different vacuum degree in every single evaporation chamber. The process is producing two different streams: v a distilled liquid without any solids and with a low polluting charge, of about the 90% of the treated quantity; v a turbid bottom containing the most of the original pollutants, of about the 10% of the treated quantity.

4) Concentrated liquid feeding The concentrated bottom of the evaporator arrives to the starting accumulation section and a pumping station feeds again this concentrated liquid to the dumping site.

5) Distilled product process stocking If further post treatments are needed, the distilled liquid is sent to a series of process tanks.

6) Osmotic membranes concentration The distilled liquid produced by the evaporators is treated on a series of osmotic membrane filters to reduce further the residual ammonia content. The osmosis permeate is collected in the accumulation tank and from here sent to the pretreatment. The permeate can also be treated and purified with activated carbons and is stored in a series of foreseen accumulation tanks.

7) Treatment on activated carbon (compulsory in presence of phenols) The distilled liquid from the evaporators, after the osmosis treatment, is sent to a series of activated carbon vessels in order to reduce further the dissolved organic substances content. The treated flow is after sent to the final product stocking tank. The spent carbon is conferred to a Company with proper authorization for its elimination and the carbon beds are, for consequence, to be changed routinely.

8) Stocking of the final treated liquid The distilled liquid, after the evaporation process and all treatments is collected in a final storage tank. In consequence of its purity, this final liquid can be classified as a liquid waste (to be conferred to a Company with authorization for its destruction) or a normal discharge that can be sent to the sewer system or to a surface water.

The following Flow-sheet is reporting all the processes employed to treat the percolate from a dumping site, for its discharge in clear river waters, complying with the Law DL 152-2006 (ex DLgs 152-1999).