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18-Env-A6 Solid Waste Engineering and Management · May 2013

Question 9 of 17: Leachate Treatment and Disposal Options

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

National Examination, May 2013 — 04-Env-A6 / 18-Env-A6, Solid Waste Engineering and Management. 3 hours duration, closed book, one letter-sized aid sheet permitted. All 17 questions constitute a complete paper (100 marks total).

Reference texts: Tchobanoglous, Theisen & Vigil, Integrated Solid Waste Management: Engineering Principles and Management Issues; Vesilind, Worrell & Reinhart, Solid Waste Engineering; Davis & Cornwell, Introduction to Environmental Engineering (6th ed.); CCME, Guidance Document on Landfill Gas Management.

Check: several questions on this paper (Q1, Q13, Q14, Q17) supply an incomplete data set and explicitly invite the candidate to "make and state" assumptions. Every assumed value below is called out where it is introduced and is chosen from standard solid-waste-engineering practice; the governing METHOD, not the specific assumed number, is what the exam is testing.

Question 9: Leachate Treatment and Disposal Options (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.

(1) Co-treatment at a municipal wastewater treatment plant — leachate is hauled by tanker truck or piped directly to the local WWTP, where it is blended (in controlled proportion, given leachate's high strength and variable toxicity) with municipal sewage and treated through the plant's existing biological process; this avoids building dedicated leachate treatment but requires the WWTP to have spare hydraulic and organic-loading capacity. (2) On-site biological treatment (aerated lagoon or sequencing batch reactor) followed by discharge or recirculation — leachate's high BOD/COD and ammonia load is reduced biologically on-site to meet a discharge permit, or the treated leachate is recirculated back into the landfill (a "bioreactor landfill" approach) to accelerate stabilization and increase gas capture.