Low temperature wastewater treatment and recycling by psychrophilic biodegradation (A case study Mexico)

Introduction. Only 27 % of the surface water in Mexico complies with the local BOD5 and COD standards. Constant desertification of the soils contributing to reduced recharge rate of the aquifers makes finding a solution to effective and wide-spread wastewater treatment a very pressing matter. The paper provides experimental data on a case study of low temperature wastewater treatment. Methods. We treated domestic (sanitary) wastewater in a continuous flow anaerobic biodigester and conducted its physicochemical evaluation during winter-spring. The treatment was done by means of a low temperature process and with a supplied influent flow volume of 20.78 L/day. Results. The first sludge formation in the initial stage showed substantial changes compared to those obtained in the final stage, where the effluent had scarce lime as a result of the microbiological activity. This transformation is seen through a removal of: 99.9 % of settleable solids (SS), 92.66 % of total solids (TS), 99.14 % of total suspended solids (TSS), 33.21 % of 5-d biochemical oxygen demand (BOD₅), 3.64 % of chemical oxygen demand (COD) with a steady pH oscillating between 8.12 and 8.72, electric conductivity (EC) within the range from 1961 µS/cm to 1785 µS/cm, temperature from 19.2 to 20.1 °C in the effluent. Conclusion. Thus, the system described is considered to be stable, easy and economic meeting the current conditions for the unloading of treated wastewater suited for agricultural reuse according to NOM-001-ECOL-1996 standard.