Onsite wastewater systems that use subsurface infiltration of septic tank effluent are used widely in the United States and abroad; however, the processes that govern effluent flow and pollutant transport during treatment in the subsurface have only recently begun to be elucidated. The conditions that often occur during intermittent wastewater application can lead to the formation and deposition of organic molecules, which can cause reduced permeability and soil pore clogging. To enhance the fundamental understanding of organic matter accumulation as affected by effluent infiltration, field research was performed at the Mines Park Test Site located at the Colorado School of Mines. Four pilot‐scale infiltration cells established in a sandy loam soil profile and used for infiltration of domestic septic tank effluent were dismantled to study the nature and extent of organic matter accumulation. Macro‐ and micromorphological observations were made, and soil samples were taken at and below the infiltrative surface and analyzed for total organic C, polysaccharides, and humic substances. Additionally, dissolved O2 concentrations were measured with time in the septic tank effluent within a cell as it infiltrated into the soil. Compared with background controls, soil samples collected at the soil infiltrative surface were characterized by high water contents and high concentrations of organic matter. The high values measured at the infiltrative surface declined sharply, however, from 1 to 2 cm of soil depth. An infiltrative surface exposed to microaerophilic concentrations (∼2 mg/L) of dissolved O2 accumulated 400 to 800% (w/w) more organic material than the mass accumulated under more continuously anaerobic conditions. The microaerophilic conditions also appeared to favor the growth of polyphosphate‐accumulating microorganisms.

ABSTRACTViable ova ofAscaris lumbricoides, an indicator organism for pathogens, are frequently found in feces-derived compost produced from ecological toilets, demonstrating that threshold levels of time, temperature, pH, and moisture content for pathogen inactivation are not routinely met. Previous studies have determined that NH3has ovicidal properties for pathogens, includingAscarisova. This research attempted to achieveAscarisinactivation via NH3under environmental conditions commonly found in ecological toilets and using materials universally available in an ecological sanitation setting, including compost (feces and sawdust), urine, and ash. Compost mixed with stored urine and ash produced the most rapid inactivation, with significant inactivation observed after 2 weeks and with a time to 99% ovum inactivation (T99) of 8 weeks. Compost mixed with fresh urine and ash achieved aT99of 15 weeks, after a 4-week lag phase. Both matrices had relatively high total-ammonia concentrations and pH values of >9.24 (pKaof ammonia). In compost mixed with ash only, and in compost mixed with fresh urine only, inactivation was observed after an 11-week lag phase. These matrices contained NH3concentrations of 164 to 173 and 102 to 277 mg/liter, respectively, when inactivation occurred, which was below the previously hypothesized threshold for inactivation (280 mg/liter), suggesting that a lower threshold NH3concentration may be possible with a longer contact time. Other significant results include the hydrolysis of urea to ammonia between pH values of 10.4 and 11.6, above the literature threshold pH of 10.

Onsite wastewater systems, widely used in the United States and abroad, often rely on infiltration of effluents into native soils for tertiary treatment and natural disinfection. The processes that govern soil clogging and hydraulic performance during infiltration into soil are complex and involve a dynamic interaction between physical, chemical, and biological processes. The authors link the development of soil clogging in onsite systems with the fundamental physical, chemical, and microbial processes that can occur during wastewater reclamation in soil environments. They provide a critical review of onsite wastewater systems, outlining the different types of wastewater-induced soil clogging, clogging locations, and clogging materials. The authors then focus on the influence of oxygen concentration on clogging and the environmental conditions that stimulate the accumulation of organic materials from microbial metabolism. Correlations are made between observational data in porous media studies and microbial metabolism. The objective of this review is to increase understanding of the processes that govern hydraulic performance of onsite wastewater systems during effluent infiltration and potentially improve system design and operation.

No abstract

No abstract