Technical evaluation and optimization of a mobile septage treatment unit.

A mobile septage treatment unit was built in India using readily available filters and membranes (mesh fabric, sand, granular activated carbon (GAC), microfilter, ultrafilter) and installed on the bed of a small truck. The target application was emptying of septic or sewage holding tanks and concentration of suspended solids while generating a liquid that could be discharged. The system was evaluated for operational and treatment performance while processing septage in the field at 108 sites in Tamil Nadu, India. After one phase of evaluation (Phase I), the system was improved and three replicate systems with slight modifications were fabricated for a second round of evaluation (Phase II) alongside the original, but modified unit. In Phase I, 105 m3 of septage was processed at an average flow of 623 L h-1 and with high removal efficiencies: 83% chemical oxygen demand (COD), 75% total suspended solids (TSS), and 98.4% total coliform (TC). In Phase II, the original and three new systems combined treated 168 m3 of septage. One of the new systems doubled in capacity and processed septage at an average flow of 2700 L h-1 while the other three averaged 1290 L h-1. The removal efficiencies in Phase II were 80% COD, 81% TSS, and 99% TC averaged between the four systems. Pass through of soluble contaminants (e.g. soluble COD, NH3-N) remain the primary challenge for treatment performance. Success may be limited with some septage due to seasonality, location, or septage age, and further validation and optimization may be necessary. However, the septage in this study was treated to local standards, and the system offers a method of onsite treatment while reducing the need of costly and often inefficient septage emptying services. Further, the system can be produced at a cost competitive to traditional septage hauling trucks.

Nutrient removal from human fecal sludge digestate in full-scale biological filters.

There is a great need for simple methods for digestate management for potential household sanitation systems based on anaerobic digestion of minimally diluted fecal waste in countries that lack safe sanitation. Herein, a full-scale three-stage filter for nitrogen and phosphorus removal from anaerobic digester effluent was implemented in Madagascar. It included a trickling filter with crushed charcoal (for aerobic nitrification), a submerged anaerobic filter with bamboo chips (for denitrification), and a submerged filter with scrap iron (for phosphorus removal). All filter materials were sourced locally. Three parallel replicate systems were operated in two sequential 8-week phases for a total of 16 continuous weeks. Though the influent feed was not as expected, with much of nitrogen in the feed coming in as organic N and not as NH3-N, the filters still removed 38-49% of total incoming nitrogen. The filters achieved high rates of nitrogen transformation along with removing solids (73-82% turbidity removal), chemical oxygen demand (67-75% removal), and phosphorus (31-50% removal). Overall, the reaction rates from this full-scale study were in line with previous lab-scale investigations with scaled-down systems, supporting their application in real-world scenarios. Based on this study, simple effluent filters can support nutrient removal for small-scale and onsite fecal sludge treatment systems.

A granular activated carbon/electrochemical hybrid system for onsite treatment and reuse of blackwater.

Over 1/3 of the global population lacks access to improved sanitation, leading to disease, death, and impaired economic development. Our group is working to develop rapidly deployable, cost-effective, and sustainable solutions to this global problem that do not require significant investments in infrastructure. Previously, we demonstrated the feasibility of a toilet system that recycles blackwater for onsite reuse as flush water, in which the blackwater is electrochemically treated to remove pathogens due to fecal contamination. However, this process requires considerable energy (48-93 kJ/L) to achieve complete disinfection of the process liquid, and the disinfected liquid retains color and chemical oxygen demand (COD) in excess of local discharge standards, negatively impacting user acceptability. Granular activated carbon (GAC) efficiently reduces COD in concentrated wastewaters. We hypothesized that reduction of COD with GAC prior to electrochemical treatment would both improve disinfection energy efficiency and user acceptability of the treated liquid. Here we describe the development and testing of a hybrid system that combines these technologies and demonstrate its ability to achieve full disinfection with improved energy efficiency and liquid quality more suitable for onsite reuse and/or discharge.

Nitrifying trickling filters and denitrifying bioreactors for nitrogen management of high-strength anaerobic digestion effluent.

The treatment of high-strength anaerobic digester effluent in laboratory-scale trickling filters for nitrification and then anaerobic filters for denitrification is reported. Five media types were investigated in the trickling filters: biochar, granular activated carbon (GAC), zeolite, Pall rings, and gravel. Three media were tested in five denitrifying filters: sand (S), bamboo wood chips (B), eucalyptus wood chips (E), bamboo with sand (B+S), and eucalyptus with sand (E+S). The different wood chips served as a supplemental electron donor for denitrification. From six months of operation, biochar, GAC, zeolite, Pall rings, and gravel media had turbidity (NTU) removal efficiencies of 90, 91, 77, 74, and 74%, respectively, and ammonia removal efficiencies of 83, 87, 85, 30, and 80%, respectively, which was primarily by nitrification to nitrate. For the anaerobic filters, S, B, B+S, E, and E+S had nitrate removal efficiencies of 30, 66, 53, 35, and 35%, and turbidity removal efficiencies of 88, 89, 84, 89, and 88%, respectively. Biochar and bamboo were selected as the best combination of media for trickling filter and anaerobic filter sequential treatment. Based on an average initial influent of 600 mg NH3-N L-1, 50 mg NO3-N L-1, and 980 NTU, the biochar filter's effluent would be 97 mg NH3-N L-1, 475 mg NO3-N L-1, and 120 NTU. The bamboo filter's final effluent would be 82 mg NH3-N L-1, 157 mg NO3-N L-1, and 13 NTU, which corresponds to 63% removal of total N and 99% removal of turbidity. These filter media thus present a simple option for sustainable post-treatment for nitrogen management and effluent polishing in low-resources settings.

On-Site Fecal Sludge Treatment with the Anaerobic Digestion Pasteurization Latrine.

The Anaerobic Digestion Pasteurization Latrine (ADPL) is a self-contained and energy neutral on-site sanitation system using anaerobic digestion of fecal sludge to generate biogas and then uses the biogas to pasteurize the digester effluent at 65-75°C to produce a safe effluent that can be reused locally as a fertilizer. Two ADPL systems were installed on residential plots with 17 and 35 residents in a peri-urban area outside of Eldoret, Kenya. Each system comprised three toilets built above a floating dome digester and one heat pasteurization system to sanitize the digested effluent. ADPLs are simple systems, with no moving parts and relying on gravity-induced flows. Adoption at the two sites was successful, and residents reported that the systems had little to no odor or flies. ADPLs were monitored for biogas production and temperatures in the pasteurization system. ADPLs serving 17 and 35 residents produced on average 16 and 11 Lbiogas/person/day (maximum of 20 and 15 Lbiogas/p/d), respectively. The temperature in the sterilization system was greater than 65°C on 58% and 87% of sampling days during the most stable period of operation. Treated effluent was analyzed periodically for chemical oxygen demand (COD), biochemical oxygen demand (BOD), total ammonia nitrogen (TAN), pH, and fecal coliform (FC). On average, the effluent at the two locations contained 4,540 and 6,450 mg COD/L (an 85% or 89% reduction of the estimated input), 2,050 and 3,970 mg BOD/L, and 2,420 and 4,760 mg NH3-N, respectively, and greater than 5 log reductions of FC (nondetectable) in the sterilization tank. Results from this field study show that anaerobic digestion of minimally diluted fecal sludge can provide enough energy to pasteurize digester effluent and that the ADPL may be a suitable option for on-site fecal sludge treatment.