UASB-septic tank as an alternative for decentralized wastewater treatment in Mexico

Abstract

The aim of this work was to evaluate the performance of a UASB-septic tank as a decentralized treatment of high-strength municipal wastewater under two different HRTs (48 and 72 h). Thus, a lab-scale (44.85 L) UASB-septic tank constituted by three compartments was operated under HRT 72 and 48 h. Removal efficiencies of total chemical oxygen demand (COD), biological oxygen demand (BOD) and suspended solids (SS) ranged from 60% to 80% for the first two parameters and from 70% to 90% for the last one. According to the statistical analysis, it was established that decreasing HRT from 72 to 48 h did not affect the performance of the UASB-septic tank; therefore, the latter HRT is recommended to be used for operation. In the first compartment, most of the organic matter removal was carried out, while the other two compartments served as polishing. Over the course of six months, the VS concentration and VS/TS ratio in sludge blanket decreased, indicating digestion and stabilization of the retained solids. Also, an increase of 4% in sludge volume was observed; thus, time for desludging would be approximately five years. Comparison of the UASB-septic tank and the UASB reactor showed that both systems had similar performance regarding effluent concentrations of organic matter and solids. Thus, under low volumetric organic load conditions (less than 20 mg COD/L h), the former is an attractive option for municipal wastewater treatment.

Comprehensive analysis of a zeolite‐packed upflow baffled septic tank using tracer tests and mathematical modelling

“…Organic matter and solids removals found in the present experiment are comparable with those reported by other authors (Ali et al, 2007; Kujawa‐Roeleveld et al, 2005; Santiago‐Díaz et al, 2018), which studied UASB‐septic tanks treating real domestic wastewater with similar arrangements, operating temperature and HRT. These results show the potential of this technology for domestic wastewater treatment in a decentralized sanitation approach.…”

“…Organic matter and solids removals found in the present experiment are comparable with those reported by other authors (Ali et al, 2007;Kujawa-Roeleveld et al, 2005;Santiago-Díaz et al, 2018) Finally, a difference between the UASB reactor and the UBST is that the latter allows sludge accumulation and stabilization. Thus, after 6 months of operation, UBST accumulated 1.5 L of sludge, equivalent to 6.7% of the effective reactor volume, and desludging should occur approximately every two years.…”

“…The UBST (Figure 1) was described previously (Santiago‐Díaz et al, 2018) and consisted of three compartments. It has 62 and 52.5 L of total and effective volume, respectively.…”

“…Nevertheless, the septic tank does not fulfill environmental regulations as its effluent commonly contains high concentrations of organic matter, nutrients and pathogens. Richards et al (2016) have demonstrated that they contribute as a source of pollution; hence, modified versions, such as the upflow baffled septic tank (UBST), have emerged, exhibiting better performance (Jorsaraei et al, 2014; Li et al, 2016; Santiago‐Díaz et al, 2018; Zha et al, 2019).…”

Pilot-scale study of a structured bed reactor for nitrogen and organic matter removal from sanitary sewage: advances and design challenges

“…Among the technologies recommended in the literature for the decentralized treatment of sanitary sewage the following can be listed: upflow anaerobic sludge-bed (UASB) reactors, septic tanks, anaerobic pond systems, trickling filters, and constructed wetlands (Moussavi et al, 2010;Santiago-Díaz et al, 2019;Singh et al, 2015). These treatment configurations remove the organic matter while nutrient compounds are slightly removed by other specific alternatives.…”