Laboratory Demonstration and Preliminary Techno-Economic Analysis of an Onsite Wastewater Treatment System

Abstract

Providing safe and reliable sanitation services to the billions of people currently lacking them will require a multiplicity of approaches. Improving onsite wastewater treatment to standards enabling water reuse would reduce the need to transport waste and fresh water over long distances. Here, we describe a compact, automated system designed to treat the liquid fraction of blackwater for onsite water reuse that combines cross-flow ultrafiltration, activated carbon, and electrochemical oxidation. In laboratory testing, the system consistently produces effluent with 6 ≤ pH ≤ 9, total suspended solids (TSS) < 30 mg L −1 , and chemical oxygen demand (COD) < 150 mg L −1 . These effluent parameters were achieved across a wide range of values for influent TSS (61−820 mg L −1 ) and COD (384−1505 mg L −1 ), demonstrating a robust system for treating wastewater of varying strengths. A preliminary techno-economic analysis (TEA) was conducted to elucidate primary cost drivers and prioritize research and development pathways toward commercial feasibility. The ultrafiltration system is the primary cost driver, contributing to >50% of both the energy and maintenance costs. Several scenario parameters showed an outsized impact on costs relative to technology parameters. Specific technological improvements for future prototype development are discussed.

Potential Pitfalls in Wastewater Phosphorus Analysis and How to Avoid Them

“…This value is similar to what we report here for total P concentrations in macerated toilet wastewater, but also aligns well with our previous report of reactive P in toilet effluent. 14 Another recent study by Reynaert et al 27 reported 36.2 mg L −1 average soluble phosphate “PO 4 ” concentration in toilet wastewater influent from a urine-diverting toilet with solids separated from the flush water. While the use of the “PO 4 ” unit is ambiguous, the analytical test used (Spectroquant) appears to give results in units of PO 4 -P. This would indicate that the average influent concentration in this study was 36.2 mg L −1 PO 4 -P or 111 mg L −1 PO 4 3− , and the nominal average concentration in the treated clean water tank is 25.4 mg L −1 PO 4 -P or 77.9 mg L −1 PO 4 3− , 27 which would be unable to meet water reuse or discharge standards with nominal effluent P concentration limits (eg, <1 mg L −1 P in India).…”

“…We reported in a previous publication total P values of system effluent of 8.3 and 21.5 “mg P L −1 ” 5 that we now suspect were measured omitting the heating step; thereby, those values represent only the orthophosphate as opposed to the total P. In a different publication, 13 we reported values of “P,” without specifying the form (which was orthophosphate) nor clarifying the reporting units (mg L −1 P). In another recent paper, 14 we did specify in the methods section that both reactive P and total P were reported in units of “mg L −1 PO 4 3− .” However, table columns and figure axes in that work were labelled only as “mg L −1 ” for both reactive P and total P. For added clarity in the future, we will explicitly include the full unit “mg L −1 PO 4 3− ” or “mg L −1 P” in all tables and figure axes, as demonstrated in the present work.…”

“… 24 , 25 Recently, an international standard ISO 30500 was specifically developed to provide performance requirements for non-sewered sanitation systems 26 and sets a minimum threshold reduction of 80% for total P. As P regulations are increasingly enforced, wastewater P content will need to be regularly measured and reported as new technologies are pilot-tested. 2 , 14 , 27 , 28 Standardized P reporting is required to compare performance across different technologies and wastewater streams to accelerate technology adoption, yet a critical gap exists due to lack of a common set of metrics. 29 This knowledge gap in reporting metrics for P and its different chemical species is also highlighted in a recent systematic review of nutrient removal and recovery technologies by Kogler et al 30 In reviewing 292 articles across 46 sources, Kogler et al 30 found that removal efficiency and achievable effluent concentrations for P removal and recovery technologies are generally underreported, with only 16% of the articles reviewed giving adequate quantitative information for meaningful interpretation of technology performance.…”

“…An intense area of research is non-sewered sanitation solutions for rural areas and low-and middle-income countries [1][2][3][4][5][6][7][8][9][10][11][12][13][14] to address the urgent need for safely-managed sanitation to improve human health and the environment. 15,16 In addition to removing pathogens and organic compounds, a key requirement of wastewater treatment is removal of nutrients including nitrogen and phosphorus (N and P) due to their potential toxic effects on aquatic environments.…”

QSDsan: an integrated platform for quantitative sustainable design of sanitation and resource recovery systems

“…A range of basic reactor configurations (e.g., continuous stirred tank reactors, CSTRs), as well as conventional (e.g., the activated sludge process) and emerging (e.g., anaerobic membrane bioreactor) technologies have been implemented in QSDsan. Additionally, a growing number of sanitation and resource recovery systems (e.g., the Biogenic Refinery, 57 the Reclaimer system 58 ) have been developed and included in the EXPOsan repository. Lists of developed process models, 59 unit operations, 60 and systems 61 can be found in QSDsan's documentation page with links to the source codes.…”