Prof Sakis Kungolos from the Department of Development and Planning, University of Thessaly, Greece visited WIT and presented a seminar on ‘Wastewater Treatment and Reuse’.
Conventional and advanced wastewater treatment consists of a combination of physical, chemical and biological processes for the removal of suspended and dissolved solids, organic matter, metals, nutrients and pathogens from wastewater. The basic physicochemical characteristics of wastewater that are taken into account for the design and operation of a wastewater treatment plant include: Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), Nitrogen and Phosphorus and microbiological parameters such as total and fecal coliforms.
Physical, chemical and biological processes are involved in wastewater treatment. Physical processes include screening, flow equalization, mixing, sedimentation, flotatiom aeration, depth filtration, membrane filtration and air stripping. Chemical processes include advanced oxidation, chemical coagulation, chemical disinfection, chemical neutralization and ion exchange. Biological processes include aerobic treatment, anaerobic treatment and anoxic treatment. In a big city, a typical wastewater treatment plant consists of the pretreatment, the primary treatment (physical and chemical processes), the secondary treatment (biological processes), the advanced or tertiary treatment and the disinfection.
A secondary (biological) wastewater treatment is applied when a wastewater reuse program is not foreseen; while for wastewater reclamation and reuse, the secondary treated wastewaters are substituted to advanced treatment processes, at a treatment level depending on the specific reuse application. The advanced treatment is used for removal of organic matter and total suspended solids beyond what can be accomplished by conventional secondary treatment processes to meet more stringent discharge and reuse requirements.
The wastewater reuse applications include agricultural irrigation, landscape irrigation (parks, golf courses, etc), non potable urban uses(fountains, toilet flushing etc), recreational/environmental uses (lakes and ponds, fisheries, snowmaking), industrial recycling and reuse (cooling towers, boiler feed, process water), indirect potable reuse through groundwater recharge. Generally advanced wastewater treatment is required before wastewater reclamation and reuse. Main concerns in wastewater reuse include protection of public health, public acceptance, the limit values for specific constituents, long term health and environmental effects, reliable treatment of wastewater to meet strict water quality requirements for a specific reuse application, risk assessment and market assessment. The disinfection method is also very important in wastewater reclamation and reuse with chlorination and ozonation being the most commonly used methods.