Microbial bioremediation and physiochemical treatment of landfill leachate

Abstract

Landfill leachate (LFL) is an environmentally hazardous waste characterised by elevated levels of organic and inorganic compounds. LFL is produced when water percolates through a landfill picking up the by-products of waste degradation. This process occurs throughout the working life of the landfill, often continuing for up to a century after the landfill is decommissioned. The discharge of untreated LFL, rich in ammonia, phosphate and nitrate, can cause the contamination of ground and surface water and the subsequent pollution of rivers, lakes and soil. As such, LFL must be collected from the bottom of the landfill and stored in tanks or lagoons before treatment. In Ireland, the treatment of LFL normally occurs off-site, as a combined treatment with domestic sewage in wastewater treatment plants (WWTPs). Although commonly practised, this process is unsuitable due to the stringent discharge limits imposed on these facilities. In light of this, the main objective of the current research was to investigate alternative options for the treatment of LFL, that were both cost-effective and had the ability to treat important LFL constituents, such as biological oxygen demand (BOD), chemical oxygen demand (COD), ammonia, nitrate and phosphate to national discharge standards. An active local landfill, Powerstown landfill, Co. Carlow, was chosen as the source of LFL for this study. Initially, microbes were isolated and characterise from LFL generated in Powerstown. Microbial strains were screened based on their ability to remediate LFL. Secondly, a variety of adsorbents, including pumice stone and oyster shells, were also screened for their ability to adsorb ammonia, phosphate and nitrate, common LFL constituents. After optimisation, both treatment options, bioremediation and adsorption, were combined into a novel fixed bed column system which was employed for the treatment of LFL on-site at Powerstown landfill. In the first instacne, a pilot study was conducted to access its ability to treat LFL. This study achieved high percentage removal rates, alonside achivign the national dichrage standard for reciving bodies. After succefully optimisation, this fixed bed system was employed on-site to LFL. This novel, cost-effctive treatment was employed for 40 day,and achieved high percentage removals of ≥81 % for BOD, COD, ammonia, phosphate and nitrate, resulting in their respective discharge limits being met. Thus, this research has proven the feasibility of a combined biological and physiochemical fixed bed system for the treatment of LFL. This system offers an exciting alternative to current treatment practices for LFL. However, additional studies are needed in order to access the ability of this treatment to successful treat LFL over longer period of time, while also taking into account the ever changing concentration of LFL.