From the above, it can be seen that Thailand does not have clear criteria regarding the quality of reclaimed water for specific purposes. As a result, international standards are suggested as a reference instead, such as ISO 20761 (‘Guidelines for water reuse safety evaluation,’ 2012) (ISO 2018b), U.S. EPA (‘guidelines for water reuse,’ 2012) (U.S. EPA 2012), WHO (‘guidelines for the safe use of wastewater (excreta and greywater),’ 2006) (WHO 2006), ‘Australian guidelines for water recycling,’ 2006 (Australian guidelines for water recycling: managing health and environmental risks (Phase 1) 2006 ), and technical guideline standards for treated wastewater reuse in Japan enacted in 2005 (Takeuchi & Tanaka 2020). When setting quality criteria for the reuse of treated wastewater, it is important to be aware of health and environmental safety, to prevent damage to the assets of the distribution, storage and end uses, and to ensure public acceptance (ISO 2018b). Table 3 compares the quality control parameters of treated wastewater from Thai WWTPs (as shown in Table 2) with the relevant reuse water safety parameters described in ISO 20761. Table 3 implies that when upgrading or installing WWTPs with regard to wastewater reclamation, more quality control parameters should be analyzed to assess the risk to health, environmental and facilities safety, especially microbial and stability parameters, which have yet to be measured by any effluent standard.
Relevant reuse water safety parameters and their differences from the Thai effluent quality control standards
| Types | Reuse water quality control parameters (ISO 2018b) | Different parameters compared with effluent std. | |
|---|---|---|---|
| Domestic WWTP | Industrial WWTP | ||
| Routine physical and chemical parameters | pH, BOD5, COD, TOC, N, P, DO, TDS, TSS, turbidity, ammonia, alkalinity, hardness, chlorine demand, residual chlorine | COD, TOC, DO, turbidity, ammonia, alkalinity, hardness, chlorine demand, residual chlorine | TOC, P, DO, turbidity, ammonia, alkalinity, hardness, residual chlorine |
| Aesthetic parameters | Color, odor | Color, odor | |
| Microbial parameters | Indicator bacteria (coliforms, E. coli, etc.) Environmental pathogens | Indicator bacteria (e.g., coliforms, E. coli) | |
| Stability parameters | -Chemical stability: specific ions (e.g., Ca2+, Mg2+, Cl−,  )-Biological stability: heterotrophic plate counts (HPC), algae, etc | Both chemical and biological stability | |
| Toxic and harmful chemicals | -Specific metal (e.g., Pb, Hg, Cd) -Oil and grease -Surfactants | Surfactants | |
| Types | Reuse water quality control parameters (ISO 2018b) | Different parameters compared with effluent std. | |
|---|---|---|---|
| Domestic WWTP | Industrial WWTP | ||
| Routine physical and chemical parameters | pH, BOD5, COD, TOC, N, P, DO, TDS, TSS, turbidity, ammonia, alkalinity, hardness, chlorine demand, residual chlorine | COD, TOC, DO, turbidity, ammonia, alkalinity, hardness, chlorine demand, residual chlorine | TOC, P, DO, turbidity, ammonia, alkalinity, hardness, residual chlorine |
| Aesthetic parameters | Color, odor | Color, odor | |
| Microbial parameters | Indicator bacteria (coliforms, E. coli, etc.) Environmental pathogens | Indicator bacteria (e.g., coliforms, E. coli) | |
| Stability parameters | -Chemical stability: specific ions (e.g., Ca2+, Mg2+, Cl−, ) -Biological stability: heterotrophic plate counts (HPC), algae, etc | Both chemical and biological stability | |
| Toxic and harmful chemicals | -Specific metal (e.g., Pb, Hg, Cd) -Oil and grease -Surfactants | Surfactants | |
BOD5, biochemical oxygen demand; COD, chemical oxygen demand; TOC, total organic carbon; DO, dissolved oxygen; TDS, total dissolved solids.