Bench scale demonstration of greywater treatment in a 3-stage sequential process comprising anaerobic, aerobic, and vertical greenery system

Non-potable reuse of treated greywater (GW) within households can reduce daily freshwater consumption and provide water security. Urban household in India was estimated to discharge 38-45 L GW/capita.day with an average composition of (mg/L) COD 238.05; total Kjeldahl nitrogen (TKN) 31.08; total phosphorus (TP) 2.85; anionic surfactants (AS) 0.5 and faecal coliform log 6.09 CFU/100 mL, etc. A 100 L/day bench-scale, 3-stage sequential GW treatment process was optimized and its long-term performance was demonstrated with synthetic GW feedstock corresponding to the aforementioned characteristics. The treatment process comprises a multi-chambered upflow anaerobic biofilm reactor (AnBR) followed by an upflow aerobic reactor (AeR) and vertical greenery system (VGS) inhabited by flowering creeper Sphagneticola trilobata. At steady-state HRT of similar to 2.25 day the process achieved the following pollutant removal (as %) COD 93.23; turbidity (NTU) 98.75; total nitrogen (TN) 54.23; TP 96.42; AS 92.97; faecal coliform: 99.95 when fed with an average influent characteristics of (mg/L) COD 281, TN: 24.41, TP 1.13, AS 16.66, faecal coliform 6 log CFU/100 mL, pH 8.85, NTU 63.3. The predominant removal of COD and AS took place in AnBR and AeR respectively, whereas, VGS demonstrated relatively higher removal of turbidity, TKN, and faecal coliforms. The inefficient nitrification-denitrification in AeR was attributed to a lower influent C/N ratio of 3.18. The acclimatization of VGS to the tertiary treatment process exhibited an aerial biomass production rate of 5063.37 mg TS/m(2).d. The treated water attained the standards for household recycling as prescribed by WHO.