Wastewater Collection and Treatment

Collecting and treating wastewater: sewers and lift stations, preliminary, primary, and secondary treatment, nutrient removal, solids handling, disinfection, and advanced treatment for reuse. The NCEES spec gives it 7–11 of 80 questions across nine subtopics — one of the larger areas.

What the problems look like

Process-train problems, often built on a schematic. Recurring shapes — infiltration vs. inflow and lift-station cycle time; sewer minimum slope and design flow with a peaking factor; bar-rack head loss; primary clarifier sizing and removal from overflow rate; activated sludge — F/M, mean cell residence time, wasting rate, SVI; trickling-filter and biotower loading; nitrogen and phosphorus removal (recycle ratios, methanol dose); a solids balance with recycle streams; digester and cake volume; chlorination and UV dose; and carbon adsorption from an isotherm or breakthrough curve. Some ask you to identify a stream or unit.

By exam day you should be able to —

• tell infiltration from inflow, and size a lift-station cycle;
• compute sewer design flow from projected population and a peaking factor;
• compute bar-rack loss, clarifier area, and expected TSS and BOD removal;
• compute θc with both the waste and effluent solids terms, and a wasting rate from SVI;
• run a nitrate balance around an anoxic zone and a methanol or carbon demand;
• close a solids balance with recycles returned at the right points;
• read a UV dose table and a GAC breakthrough curve.

Where people lose points

• Trace the streams. RAS vs. WAS, which recycle rejoins ahead of which unit, where the RAS actually returns in this plant — the textbook layout isn't always the one drawn.
• θc terms — include effluent solids; waste drawn from the return line is at the underflow concentration, not MLSS; V/Qw holds only when wasting from the basin and effluent solids are neglected.
• Clarifier removal table — read the column for the stated overflow rate (lower rate, higher removal), and don't swap the TSS and BOD₅ rows.
• Stoichiometry basis — nitrate as NO₃⁻ vs. as N; methanol vs. other carbon sources.
• Logs and exponents — natural log in the fixed-film equation; recover q with the exponent 1/n.
• Table lookups — right bar shape, right organism column, right log-credit row.
• Chlorine chemistry — in an ammonia-bearing effluent the first residual is combined, and bisulfite reduces chloramines too.

Have these at your fingertips

The activated-sludge relations, the primary-clarifier removal table, bar-rack loss, the UV dose table, and the chloramine and dechlorination reactions — plus where they live in the Handbook. Design-standard questions (minimum sewer slope, screening, redundancy) draw on Ten States Standards — Wastewater Facilities, 2014 edition, on the list both before and after the April 2027 change.

Going deeper

• WRE design standards: the April 2027 change
• Analysis and Design — loading and mass-balance tools
• Surface Water and Groundwater Quality

Part of the Water Resources & Environmental exam. Practice this area with exam-real problems — the tutor walks any one you miss. → Start practicing free — free with an account.