Possibilities for sustainable nutrient recycling by faecal separation combined with urine

Household wastewater can be divided into three fractions by origin; urine, faeces and greywater. The largest nutrient and smallest heavy metal contents are found in the urine, which is easily collected separately using a urine-diverting toilet. The second most nutrient-containing fraction is the faecal matter. This fraction (faeces and toilet paper) has the smallest mass of the three, approximately 60 kg of wet weight per person and year. The nutrients in the urine and faeces have to be recycled to agriculture for society to be sustainable. The faecal matter can either be collected dry or, after a short waterborne transport, be separated from the flushwater in a separator that uses a combination of whirlpool effect, gravity and surface tension. Using this type of separation, between 58% and 85% of the faecal nutrients were separated in the measurements performed here. By recycling the urine and the faecal nutrients, much energy can be saved as the load on the wastewater treatment plant decreases and as mineral fertilisers are replaced in agriculture. To avoid transmission of diseases, the faecal matter has to be sanitised before recycling. If the faecal matter is collected dry, it is possible to perform the sanitation by thermal composting, preferably together with household biodegradable waste. A calculation method for determination of the safety margins for sanitation was developed. In a pilot-scale study, the safety margin for thermal composting of faeces and food waste, with old compost as an amendment, was approximately 37 times total inactivation of Enteroviruses, the most thermotolerant organism evaluated. Another sanitation method investigated was chemical disinfection using urea or peracetic acid. At a dosage between 0.5% and 1.0%, the highly reactive peracetic acid inactivated all investigated organisms within 12 hours of treatment. The high dry matter content (10% DM) meant that high dosages were needed. Lower dry matter content would decrease the dosage required for proper sanitation. A very promising treatment was the addition of urea. Addition of 30 g ureanitrogen per kg of wet weight faecal matter resulted in total inactivation of the monitored organisms, E. coli, Salmonella spp, Enterococcus spp, Salmonella typhimurium 28B phage and Ascaris suum eggs, within 50 days of treatment at 20°C. The spore-forming bacteria Clostridium spp in its dormant state was resistant to this treatment. As the urea has to be degraded to ammonia before it functions as a disinfectant, there is some delay in this treatment. Therefore, urea addition followed by 2 months storage is the preferred treatment for disinfection of separated faecal matter. As additional effects, urea increases the fertiliser value of the treated material and there is no risk of microbial regrowth. Changing to urine-diversion combined with faecal separation and disinfection by urea seems to be an interesting way to decrease the resource usage and possibly improve the hygienic standard of wastewater systems

Actions needed before insects can contribute to a real closed-loop circular economy in the EU

Insects are the waste managers of nature and could play a vital role in closing the loop of nutrients from society back into the food industry and thereby reduce the environmental impact of our food production system, as is the aim of EU's Farm to Fork strategy. Insects can be used to convert biodegradable waste into their own biomass that can be used as food or in animal feed, thus linking waste management to food production. However, food safety regulations prevent the use of around 70% of available food waste in the EU as rearing substrate for insects. To tap into the true environmental benefits of insects as an alternative protein source, they have to be reared on mixed food waste. The main reason for the food safety regulation is the outbreak of Mad Cow disease (BSE) in the 1980s, caused by prions (misfolded proteins). The circular system that gave rise to Mad Cow disease is the most closed loop system possible. Using insects in waste management to convert bio-waste into animal feed does not entail such a closed loop system, but rather introduces an extra barrier to disease transmission. In order to fully tap into the benefits of insects as an alternative protein source, it is crucial that funds are allocated to determine whether prions are truly a risk in a circular insect food production system

Degradation of poly-L-lactic acid biopolymer films in Ca(OH)2-dosed fresh human urine collected in source-separating sanitation systems

Alkaline dehydration is a promising technology for producing organo-mineral fertiliser from source-separated human urine, but potential risks to users from handling alkaline earth hydroxides at source and carbonation of hydroxides during dehydration limit its implementation in real-life settings. These issues could be addressed by enclosing chemicals in bio-derived polymers. In this study, we investigated degradation and erosion of poly-L-lactic acid (PLLA) biopolymer films of different thicknesses (0.05, 0.1 and 0.25 mm) in Ca(OH)2-dosed fresh urine and Milli-Q water at two temperatures (20 degrees C and 45 degrees C). Evaluation of degraded films by XRD, GPC and SEM showed changes in crystallinity, reduction in molecular weights and change in surface morphology, respectively. SEM/EDX, FTIR and ICP-OES data indicated that L-CaL2, L-lactides and lactic acid were formed in urine. Overall, we found that thinner films, higher temperature and higher pH accelerated PLLA degradation in urine

Resource recovery technologies as microbial risk barriers: towards safe use of excreta in agriculture based on hazard analysis and critical control point

Agricultural use of human excreta contributes to sustainable nutrient resource management. In contrast, resource recovery from human excreta is associated with the risk of infection by pathogenic microorganisms. The microbial risk associated with human excreta needs to be properly managed. Pathogen inactivation efficacy of resource recovery technologies should be evaluated so that individual resource recovery processes can be monitored as health risk barriers. To this end, we reviewed the sanitization potential of resource recovery technologies from human excreta and identified the monitoring parameters of hazard analysis and critical control point (HACCP). We describe the inactivation of surrogate microorganisms in selected technologies in terms of the physicochemical conditions of matrices, different tolerances among surrogate microorganisms, and inactivation mechanisms. The estimated storage/operating time required to achieve the target log reduction values (LRVs) is shortened in thermal processes such as thermophilic storage, drying, composting, microwaving, and thermophilic digestion. In most processes, phage and helminth eggs were found to be appropriate indicators for conservative estimation. Finally, we argue that sanitization is congruent with decomposition of readily degradable organic matter and resource recovery. The barrier efficacy of resource recovery technologies should be validated using a pathogen inactivation kinetics model so that the exposure risk to infectious pathogens is sufficiently reduced through a reasonable combination of non-treatment and non-technical health risk barriers

Process efficiency in relation to enzyme pre-treatment duration in black soldier fly larvae composting

Black soldier fly larvae (BSFL) composting is a treatment in which biodegradable food waste is converted into animal-feed protein and organic fertiliser. BSFL composting has greatest potential for mixed food waste, but under European Union regulations only plant-based waste is permitted as feed for larvae. Biomass conversion efficiency (BCE) in BSFL composting is lower for plant-based waste than for mixed food waste. One way of improving BCE for plant-based waste is to add enzymes to make the waste more available to the larvae, but enzyme pre-treatment is not commonly applied prior to BSFL composting. Therefore this study examined the impact of enzyme pre-treatment duration on process efficiency in BSFL composting of lettuce-cabbage waste pretreated with enzymes for 0-4 days. The results showed that total solids (TS) in larvae decreased with longer enzyme pre-treatment. Direct addition of enzymes at the start of BSFL treatment (0 day pre-treatment) resulted in 22% higher BCE on a volatile solids (VS) basis compared with the control, while longer pre-treatment did not improve BCE further. Much of the VS was respired in the 0-day pre-treatment, resulting in lower mass of residues at the end of treatment. Longer pre-treatment increased microbial respiration, suggesting that the microbial community consumed more easily available carbohydrates during the pre-treatment step, which counteracted the purpose of enzyme pre-treatment, i.e. increasing BCE during BSFL composting

Fate of Ascaris at various pH, temperature and moisture levels

Soil-transmitted helminths (STH) are intestinal worms that infect 24% of the world’s population. Stopping the spread of STH is difficult, as the eggs are resilient (can withstand high pH) and persistent (can remain viable in soils for several years). To ensure that new sanitation systems can inactivate STH, a better understanding of their resilience is required. This study assessed the inactivation of Ascaris eggs under various conditions, in terms of moisture content (MC) (90%), temperature (20–50 C) and pH (7–12.5). The results highlight that the exposure of Ascaris eggs to elevated pH (10.5–12.5) at temperatures 27.5 C for >70 days had no effect on egg viability. Compounding effects of alkaline pH (10.5) or decreasing MC (<20%) was observed at 35 C, with pH having more of an effect than decreasing MC. To accelerate the inactivation of STH, an increase in the treatment temperature is more effective than pH increase. Alkaline pH alone did not inactivate the eggs but can enhance the effect of ammonia, which is likely to be present in organic wastes

Process efficiency and greenhouse gas emissions in black soldier fly larvae composting of fruit and vegetable waste with and without pre-treatment

One technology that implements circular economy principles is black soldier fly larvae (BSFL) composting. To assess the environmental impact of BSFL technology, more data on emissions of greenhouse gases (GHG) and ammonia are needed. This study investigated process efficiency and GHG emissions from BSFL composting of orange peels and a mix of broccoli and cauliflower trimmings, with and without pre-treatment. Two weeks of substrate pre-treatment with ammonia or fungi (Trichoderma reesei) were investigated, and direct emissions of GHG and ammonia from the process were evaluated. Process efficiency was evaluated by waste-to-biomass conversion efficiency (BCE) and material reduction. In BSFL composting of trimmings, BCE was not significantly improved by pre-treatment, However, larval volatile solids (VS) load in the fungi pre-treated treatment was very low, likely contributing to low BCE. BCE was low (6%) in the peel control and even lower in the pre treatments, indicating that this substrate is unsuitable for BSFL composting. Material reduction was largest for trimmings (84%) and peels (60%) pre-treated with fungi. Emissions of methane (CH4) and nitrous oxide (N2O), expressed in CO2-eq, were very low (0.04-1.57 g/kg initial wet weight (ww)) compared with direct CO2 emissions (47-147 g/kg initial ww). Fungi pre-treatment appeared to make the trimmings more available to the larvae, while also drying out the substrate and removing a large proportion of available VS. Thus fungi pretreatment could be used to increase waste treatment capacity. Ammonia pre-treatment reduced emissions of CH4 and N2O without affecting overall BCE, but significantly increased NH3 emissions

Alkaline dehydration of source -separated fresh human urine: Preliminary insights into using different dehydration temperature and media

For sanitation systems aiming at recycling nutrients, separately collecting urine at source is desirable as urine contains most of the nutrients in wastewater. However, reducing the volume of the collected urine and recovering majority of its nutrients is necessary, as this improves the transportability and the end-application of urine-based fertilisers. In this study, we present an innovative method, alkaline dehydration, for treating fresh human urine into a nutrient-rich dry solid. Our aim was to investigate whether fresh urine (pH11) could be dehydrated at elevated temperatures (50 and 60 °C) with minimal loss of urea, urine's principal nitrogen compound. We found that it was possible to concentrate urine 48 times, yielding dry end-products with high fertiliser value: approximately, 10% N, 1% P, and 4% K. We monitored the physico-chemical properties and the composition of various dehydration media to provide useful insights into their suitability for dehydrating urine. We demonstrated that it is possible to recover >90% nitrogen when treating fresh urine by alkaline dehydration by inhibiting the enzymatic hydrolysis of urea at elevated pH and minimisingthe chemical hydrolysis of urea with high urine dehydration rates

Factors influencing physicochemical characteristics of faecal sludge in Phnom Penh, Cambodia

Comprehensive knowledge of faecal sludge characteristics is needed for sludge management planning, but it is lacking for the city of Phnom Penh, Cambodia. Thus, this study characterised physicochemical properties of faecal sludge from households in Phnom Penh and related these to sludge containment unit type, unit age, connectedness to the urban drainage network, type of wastewater captured, watertight containment units, number of users, and emptying practices. In total, 194 faecal sludge samples collected during containment unit emptying were analysed for physicochemical parameters. Information on containment units was collected in a survey of emptiers and users. Mean values of faecal sludge chemical parameters were found to be slightly lower than previously reported values for low-/middle-income countries, whereas physicochemical properties were within similar ranges. The main factor influencing organic matter content in faecal sludge was containment unit connection to the urban drainage network, whereas emptying practice and capture of only blackwater affected nutrient levels. The concentrations of nutrients and organic pollutants greatly exceeded Cambodian discharge standards for wastewater. This causes environmental impacts, so treatment is needed before discharge. The faecal sludge characteristics and influencing factors identified here can serve as a baseline for sanitation stakeholders planning faecal sludge management systems in Phnom Penh and similar cities