Question 5 of 18: Factors in Discharging Landfill Leachate to a WWTP

Question 5: Factors in Discharging Landfill Leachate to a WWTP (4 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

Discharging landfill leachate to a municipal wastewater treatment plant (co-treatment) is a common and often cost-effective option, but it has to be assessed against several factors before it is approved. Leachate strength versus plant treatability: leachate typically carries high BOD/COD, ammonia-nitrogen, and in older leachate a fraction of poorly biodegradable (recalcitrant) organics and dissolved metals; the receiving plant's biological process (especially its nitrification capacity, which ammonia can inhibit at high loading) has to be checked against this load. Hydraulic and organic loading capacity: the leachate flow and mass loading must be small relative to the plant's design capacity and current headroom, or it will shock-load the process; equalization storage at the landfill is often required to spread deliveries evenly. Sewer-use bylaw and receiving-plant permit limits: the local sewer-use bylaw sets numeric limits on pH, metals, sulfide and other inhibitory or corrosive substances, and the plant's own discharge permit (effluent quality, biosolids quality for land application) constrains what it can accept without violating its own limits. Pretreatment needs: depending on the gap between raw leachate quality and what the bylaw/plant can accept, pretreatment such as equalization, metals precipitation or ammonia stripping/air stripping may be required before discharge. Logistics and cost: whether leachate is piped directly or trucked, the trucking/tipping cost versus on-site treatment, and the effect of variable leachate flow (wet-season peaks) on the transport/receiving arrangement.