Landfill runoff water and landfill leachate discharge and treatment

Abstract

The continuously increasing requirements for environmental protection create problems for many countries in treating landfill runoff water. In the present paper, the creation, chemical composition and treatment possibilities for leachate in 5 Estonian landfills are studied. Generally, the younger the landfill, the higher concentrations of pollutants. In the Vaatsa landfill, the landfill runoff water flow rate has been measured up to 150 m3/d, average flow (Qaverage) = 10–20 m3/d. The composition of pollutants in the leachate depends on the character of the deposited waste material and on the age of the landfill. In Vaatsa landfill, the leachate biochemical oxygen demand (BOD7) is in the limits of 300–960 mgO2/l, in Uikala landfill the leachate BOD7 is in the limits of 231–1750 mgO2/l, but in Tallinn landfill it can reach up to 5500 mgO2/l, chemical oxygen demand (COD) is 580–2390 mgO/l and 9100 mgO/l correspondingly. Ammonia nitrogen in Vaatsa is between 50–330 mgN/l, in Uikala it is between 427–729 mgN/l, but it can reach up to 970 mgN/l in Tallinn. Total nitrogen (Ntot) in Vaatsa is 130–470 mgN/l and 1335 mgN/l correspondingly, and in Uikala 564–1567 mgN/l. The content of heavy metals is relatively low, caused by the high content of sulphates (500 – 700 mg/l), causing rapid sedimentation of heavy metals from the leachate. In the older landfills, the efficiency of nanofiltration (NF) and reverse osmosis (RO) were investigated, and the rather good results were obtained for BOD7 and COD. After RO treatment, the results were as follows: COD of 57 mgO/l, BOD7 of 35 mgO2/l. RO was able to reduce COD and BOD7 of biologically treated leachate by 97.9% and 93.2%. NF reduced 98 and 41% of leachate COD and BOD7. Neither RO nor NF was able to reduce the total nitrogen to the required discharge limit of 15 mg/l.