Question 2 of 18: Assessing Compatibility of Industrial Wastewater With a Municipal Activated-Sludge Plant

Question 2: Assessing Compatibility of Industrial Wastewater With a Municipal Activated-Sludge Plant (5 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.

Before recommending co-treatment, the investigation has to establish three things: whether the biology can survive and process the added waste, whether the plant has enough hydraulic and organic capacity, and whether the combined effluent will still meet the permit. First, characterize the industrial wastewater — flow rate and its diurnal/seasonal variability, BOD₅/COD, TSS, pH, temperature, nutrient content (N and P, since industrial waste is often nutrient-deficient relative to its carbon load), and screen specifically for constituents toxic or inhibitory to biological treatment: heavy metals, cyanide, phenols, surfactants, oil and grease, and any priority pollutants. Second, run bench- or pilot-scale biological treatability/toxicity testing (e.g. respirometry, a bioassay on the activated-sludge organisms themselves) at the anticipated blended concentration, to confirm the waste is biodegradable and non-inhibitory rather than simply assuming it because it is "organic." Third, verify the existing plant's hydraulic and organic loading capacity (design vs. current flow, BOD and TSS loading margin, aeration/oxygen-transfer capacity, clarifier and digester capacity) against the added flow and load. Fourth, compare the predicted combined effluent quality (via a mass-balance blend of the two waste streams through the expected removal efficiency) against every parameter in the discharge permit, not just BOD/TSS — metals, ammonia, and any industry-specific parameters (e.g. phenol, cyanide) that the permit may separately limit. Finally, confirm any local sewer-use bylaw pretreatment limits the industry must meet before discharge to the collection system, since a municipality typically requires pretreatment for anything that could upset the plant regardless of what the receiving-water permit ultimately allows.