A new computational control strategy for leachate management in bioreactor landfills

A novel computational measurement-based control strategy (CMCS) was developed to manage leachate recirculation based on monitoring ofkey system parameters. The proposed framework identifies the operational phase ofthe controlled bioreactor, and accordingly determines quantities ofleachate, buffer, supplemental water, and nutritional amendments required to provide the temporally changing landfill microbial consortia with their growth requirements. The CMCS was tested in a pilot-scale bioreactor cell (0.5 m3) for a period of nine months, and compared to a conventional open-loop leachate control scheme (fixed recirculation rate of produced leachate) in an identical cell. Overall, positive results confirmed the applicability and benefits of the control strategy to optimize the leachate recirculation and manipulation processes. Throughout the 21 operational cycles of the controlled bioreactor cell, the maximum specific daily recirculation volume (24 L/t/d) was sixfold the minimum volume determined. The amounts of inoculum/nutrient, buffer, and supplemental water were also computed cyclically, and ranged between 2% and 11%, 1% and 9%, and 3% and 16% of the total volume recycled, respectively. The recirculated volumes of leachate and other amendments were highly variable, and did not follow any predictable trends. In general, CMCS achieved proper control with a minimal use of resources, e.g. it utilized about 55% less buffer compared with the leachate neutralization practice commonly used in lab- and pilot-scale studies. The greater degradation rates of organic matter combined with relative increases in biogas production (1.7-fold greater) demonstrate that calculation-based recirculation stimulated the methanogenic activity and accelerated the bioreactor evolution.