A tool to evaluate the fertiliser value and the environmental impact of substrates from wastewater treatment

State of the art of urine treatment technologies: A critical review

Over the last 15 years, urine treatment technologies have developed from lab studies of a few pioneers to an interesting innovation, attracting attention from a growing number of process engineers. In this broad review, we present literature from more than a decade on biological, physical-chemical and electrochemical urine treatment processes. Like in the first review on urine treatment from 2006, we categorize the technologies according to the following objectives: stabilization, volume reduction, targeted N-recovery, targeted P-recovery, nutrient removal, sanitization, and handling of organic micropollutants. We add energy recovery as a new objective, because extensive work has been done on electrochemical energy harvesting, especially with bio-electrochemical systems. Our review reveals that biological processes are a good choice for urine stabilization. They have the advantage of little demand for chemicals and energy. Due to instabilities, however, they are not suited for bathroom applications and they cannot provide the desired volume reduction on their own. A number of physical-chemical treatment technologies are applicable at bathroom scale and can provide the necessary volume reduction, but only with a steady supply of chemicals and often with high demand for energy and maintenance. Electrochemical processes is a recent, but rapidly growing field, which could give rise to exciting technologies at bathroom scale, although energy production might only be interesting for niche applications. The review includes a qualitative assessment of all unit processes. A quantitative comparison of treatment performance was not the goal of the study and could anyway only be done for complete treatment trains. An important next step in urine technology research and development will be the combination of unit processes to set up and test robust treatment trains. We hope that the present review will help guide these efforts to accelerate the development towards a mature technology with pilot scale and eventually full-scale implementations.

Qualitative Risk Analysis for Contents of Dry Toilets Used to Produce Novel Recycling Fertilizers

Human excreta are a sustainable, economical source of nutrients, and can be used to produce recycling fertilizer for horticulture by collecting and processing the contents of dry toilets. Herein, we discuss the key categories of risk associated with the main groups of materials commonly found in dry toilets. The study was part of the development of a German product standard for marketable and quality-assured recycling fertilizers from human excreta for use in horticulture. Particular attention is paid to ensuring that the fertilizer is epidemiologically and environmentally harmless and that the quality of the recycling fertilizer is adequate in terms of low pollution and nutrient availability. In sum, the risk of transmissible human pathogens lies within the human excreta, particularly feces; plant materials added during composting are of particular phytosanitary relevance; pharmaceutical residues in excrements and chemical additives are potential sources of pollutants; non-biodegradable contaminants can cause pollution and injury; and the horticultural risks involve mainly the ammonia emission potential and in some cases the salinity effects of urine. These risks can be reduced significantly (i) with education of users around proper operation of dry toilets and the consequences of adding inappropriate waste, (ii) with facilitation of proper use with general waste bins and clear instructions, and importantly (iii) by using modern sanitization and cleaning processes and testing for harmful substances under the guidance of local laws and regulations, ensuring safe and high-quality fertilizers. In conclusion, the benefits of using dry toilet contents to produce fertilizers for use in horticulture are unquestionable. Our analysis highlights the need to support recycling optimization and awareness for the purpose of a sustainable circular economy and to minimize the risk of harm to humans and the environment overall.

Micropollutant removal in an algal treatment system fed with source separated wastewater streams

Micropollutant removal in an algal treatment system fed with source separated wastewater streams was studied. Batch experiments with the microalgae Chlorella sorokiniana grown on urine, anaerobically treated black water and synthetic urine were performed to assess the removal of six spiked pharmaceuticals (diclofenac, ibuprofen, paracetamol, metoprolol, carbamazepine and trimethoprim). Additionally, incorporation of these pharmaceuticals and three estrogens (estrone, 17β-estradiol and ethinylestradiol) into algal biomass was studied. Biodegradation and photolysis led to 60-100% removal of diclofenac, ibuprofen, paracetamol and metoprolol. Removal of carbamazepine and trimethoprim was incomplete and did not exceed 30% and 60%, respectively. Sorption to algal biomass accounted for less than 20% of the micropollutant removal. Furthermore, the presence of micropollutants did not inhibit C. sorokiniana growth at applied concentrations. Algal treatment systems allow simultaneous removal of micropollutants and recovery of nutrients from source separated wastewater. Nutrient rich algal biomass can be harvested and applied as fertilizer in agriculture, as lower input of micropollutants to soil is achieved when algal biomass is applied as fertilizer instead of urine.

Environmental Benefits and Burdens of Phosphorus Recovery from Municipal Wastewater

The environmental benefits and burdens of phosphorus recovery in four centralized and two decentralized municipal wastewater systems were compared using life cycle assessment (LCA). In centralized systems, phosphorus recovered as struvite from the solids dewatering liquid resulted in an environmental benefit except for the terrestrial ecotoxicity and freshwater eutrophication impact categories, with power and chemical use offset by operational savings and avoided fertilizer production. Chemical-based phosphorus recovery, however, generally required more resources than were offset by avoided fertilizers, resulting in a net environmental burden. In decentralized systems, phosphorus recovery via urine source separation reduced the global warming and ozone depletion potentials but increased terrestrial ecotoxicity and salinization potentials due to application of untreated urine to land. Overall, mineral depletion and eutrophication are well-documented arguments for phosphorus recovery; however, phosphorus recovery does not necessarily present a net environmental benefit. While avoided fertilizer production does reduce potential impacts, phosphorus recovery does not necessarily offset the resources consumed in the process. LCA results indicate that selection of an appropriate phosphorus recovery method should consider both local conditions and other environmental impacts, including global warming, ozone depletion, toxicity, and salinization, in addition to eutrophication and mineral depletion impacts.

Greenhouse evaluation and environmental impact assessment of different urine-derived struvite fertilizers as phosphorus sources for plants

A selection of six urine-derived struvite fertilizers generated by innovative precipitation technologies was assessed for their quality and their effectiveness as phosphorus sources for crops. Struvite purity was influenced by drying techniques and magnesium dosage. In a greenhouse experiment, the urine fertilizers led to biomass yields and phosphorus uptakes comparable to or higher than those induced by a commercial mineral fertilizer. Heavy metal concentrations of the different struvite fertilizers were below the threshold limits specified by the German Fertilizer and Sewage Sludge Regulations. The computed loading rates of heavy metals to agricultural land were also below the threshold limits decreed by the Federal Soil Protection Act. Urine-derived struvite contributed less to heavy metal inputs to farmland than other recycling products or commercial mineral and organic fertilizers. When combined with other soil conditioners, urine-derived struvite is an efficient fertilizer which covers the magnesium and more than half of the phosphorus demand of crops.

Urine--a valuable fertilizer with low risk after storage in the tropics

Urine contains a considerable amount of nutrients and potentially could be used as supplement commercial mineral fertilizer; however, it carries risk of contamination. The effect of urine storage as a simple treatment method was examined under tropical conditions. Initial concentrations of total coliforms (2.3 x 10(5) CFU/100 mL), E. coli (<1.0 x 10(4) CFU/100 mL), and Salmonella sp. were less than detection limit after four weeks. Open storage led to nitrogen losses of 90%, whereas closed storage containers retained 93% of total nitrogen. Under storage, the N:P ratio of 8:1 in fresh urine changed to 14:1 in the supernatant and to 1:12 in the precipitate, and 100% of magnesium and 96% of calcium was precipitated. A model showed that, depending on plant requirements, using the mixture of supernatant and precipitate as fertilizer for crops such as cassava was reasonable. To fertilize crops such as rice, however, additional P and K was needed. The nutrient-based flux of heavy metals to soils was negligible.

Fertiliser products from new sanitation systems: their potential values and risks

The plant nutrients consumed in human society today are lost through the established wastewater treatment systems in industrialised countries as well as via insufficient or non-existent handling of sewage in the developing world. New sanitation systems have been designated to overcome this failure. The source separated wastewater streams collected within these systems contain a high nutrient content, and can be used as fertiliser as well as soil conditioner after appropriate storage and/or treatment. Application in agriculture with existing techniques is feasible. However, pathogens and pharmaceuticals contained in these fertiliser types are a potential hazard. Nevertheless, storage and appropriate treatment can minimise the risks. The products deriving from these systems have a high potential to preserve available plant nutrient resources and deficiencies in agriculture as well as being able to substitute synthetic plant nutrients and at the same time prevent unwanted environmental nutrient over-enrichment.