Wastewater Treatment and Collection
Wastewater Treatment and Collection tests process control and collection-system stewardship: influent characterization, secondary treatment, disinfection, solids handling, and the sanitary sewer's capacity to keep sewage out of basements and waterbodies.
Treatment
Primary treatment removes settleable solids; secondary biological treatment (activated sludge, trickling filters, RBCs, lagoons) removes BOD and TSS. The federal secondary standard is 30 mg/L BOD5 and 30 mg/L TSS with at least 85% removal, but your NPDES permit governs. Many New Hampshire permits add seasonal ammonia or nitrogen limits (Great Bay), phosphorus limits (Lake Winnipesaukee), and chlorine residual limits, requiring nitrification and dechlorination.
Solids handling-thickening, digestion, dewatering-matters because return liquor sends ammonia and solids back to the headworks.
Collection
Collection systems must control infiltration/inflow, grease, roots, and sediment; lift stations need backup power, alarms, and run-time records. Sanitary sewer overflows must be reported to NHDES and the public under state SSO requirements; bypassing without notification is a violation.
Worked example
Influent BOD5 240 mg/L, effluent 16 mg/L. Removal = (240 − 16) ÷ 240 × 100 = 93.3%. If flow is 0.5 MGD, load removed = 0.5 × 8.34 × (240 − 16) = 934 lb/day. Percent removal alone can hide an overload: a plant can remove 90% and still exceed 30 mg/L if influent is 400 mg/L.
Traps
Reporting concentration when the permit limits load (lb/day), ignoring return flows, treating a lift-station high-level alarm as a nuisance, and assuming secondary limits are the only limits-ammonia, phosphorus, and chlorine are common New Hampshire add-ons.