Tove A. Larsen

Separate management of anthropogenic nutrient solutions (human urine)

Anthropogenic Nutrient Solution (ANS, Urine) adds about 75% of the nitrogen and 50% of the phosphorus to domestic wastewater. It is proposed to collect ANS at the source and release it sequentially, so that it arrives all at the same time at the treatment plant where it could be treated separately. The proposed system would have many advantages relative to the conventional technology. A stepwise transition from the conventional to the proposed technology would slowly improve system performance.

Urea hydrolysis and precipitation dynamics in a urine-collecting system.

Blockages caused by inorganic precipitates are a major problem of urine-collecting systems. The trigger of precipitation is the hydrolysis of urea by bacterial urease. While the maximum amount of precipitates, i.e. the precipitation potential, can be estimated with equilibrium calculations, little is known about the dynamics of ureolysis and precipitation. To gain insight in these processes, we performed batch experiments with precipitated solids and stored urine from a urine-collecting system and later simulated the results with a computer model. We found that urease-active bacteria mainly grow in the pipes and are flushed into the collection tank. Both, bacteria and free urease, hydrolyse urea. Only few days are necessary for complete urea depletion in the collection tank. Two experiments with precipitated solids from the pipes showed that precipitation sets in soon after ureolysis has started. At the end of the experiments, 11% and 24% of urea was hydrolysed while the mass concentration of newly formed precipitates already corresponded to 87% and 97% of the precipitation potential, respectively. We could simulate ureolysis and precipitation with a computer model based on the surface dislocation approach. The simulations showed that struvite and octacalcium phosphate (OCP) are the precipitating minerals. While struvite precipitates already at low supersaturation, OCP precipitation starts not until a high level of supersaturation is reached. Since measurements and computer simulations show that hydroxyapatite (HAP) is the final calcium phosphate mineral in urine solutions, OCP is only a precursor phase which slowly transforms into HAP.

The concept of sustainable Urban Water Management

Urban Water Management involves the fields of water supply, urban drainage, wastewater treatment and sludge handling. On the basis of the Agenda 21, principles and guidelines for sustainable urban water management are discussed. Sustainable technology leads to acceptable gradients in state variables. New technologies departing from an analysis of required services rather than stepwise improvement of existing technology is preferred. An efficient use of resources will lead to a minimal increase of entropy and will require an active rather than a reactive approach. The analysis of the transition period from todays to a sustainable situation is important. An example is introduced which deals with global cycling of nutrients and which may be approached on a regional scale.

Estimating the precipitation potential in urine-collecting systems

Precipitation in urine-separating toilets (NoMix toilets) and waterless urinals causes severe maintenance problems and can strongly reduce the content of soluble phosphate. In this study, we present a computer model for estimating the precipitation potential (PP) in urine-collecting systems. Calculating the PP enables to predict the composition and mass concentration of precipitates. We used our computer model for investigating how urea hydrolysis and dilution with flushing water affect precipitation. In a previous study, we found that microbial urea hydrolysis (ureolysis) triggers precipitation and that the amount of precipitates is limited by calcium and magnesium. With the present simulations, we could confirm these findings. We determined that only a small fraction of urea has to be hydrolysed for reaching 95% of the maximum PP. Since urease-positive bacteria are abundant in urine-collecting systems, strong precipitation is very likely. In further simulations, we determined that struvite (MgNH(4)PO(4).6H(2)O) and hydroxyapatite (HAP, Ca(10)(PO(4))(6)(OH)(2)) are the main precipitate compounds. If urine is highly diluted with tapwater, calcite (CaCO(3)) occurs as well. HAP is the only calcium phosphate mineral, although several others were supersaturated. Additionally, the simulations indicated that urine dilution diminishes the risk of blockages, since the mass concentration of precipitates decreases with the volume of flushing water. Rainwater flushing is more effective than flushing with tapwater. Moreover, flushing with tapwater leads to high phosphate fixation, because the total amount of calcium and magnesium ions increases, while the total amount of phosphate keeps constant. Finally, we compared simulation results with field measurements and found good agreement at low and very high urine dilution.

Emerging solutions to the water challenges of an urbanizing world

The top priorities for urban water sustainability include the provision of safe drinking water, wastewater handling for public health, and protection against flooding. However, rapidly aging infrastructure, population growth, and increasing urbanization call into question current urban water management strategies, especially in the fast-growing urban areas in Asia and Africa. We review innovative approaches in urban water management with the potential to provide locally adapted, resource-efficient alternative solutions. Promising examples include new concepts for stormwater drainage, increased water productivity, distributed or on-site treatment of wastewater, source separation of human waste, and institutional and organizational reforms. We conclude that there is an urgent need for major transdisciplinary efforts in research, policy, and practice to develop alternatives with implications for cities and aquatic ecosystems alike.

High acceptance of urine source separation in seven European countries: a review.

Urine source separation (NoMix-technology) is a promising innovation aiming at a resource-oriented, decentralized approach in urban water management. However, NoMix-technology has a sensitive end-point: peoples bathrooms. NoMix-technology is increasingly applied in European pilot projects, but the success from a user point-of-view has rarely been systematically monitored. We aim at closing this gap. We review surveys on acceptance, including reuse of human urine as fertilizer, from 38 NoMix-projects in 7 Northern and Central European countries with 2700 respondents. Additionally, we identify explanatory variables with logistic regression of a representative Swiss library survey. NoMix-technology is well accepted; around 80% of users liked the idea, 75-85% were satisfied with design, hygiene, smell, and seating comfort of NoMix-toilets, 85% regarded urine-fertilizers as good idea (50% of farmers), and 70% would purchase such food. However, 60% of users encountered problems; NoMix-toilets need further development. We found few differences among countries, but systematic differences between public and private settings, where people seem more critical. Information was positively correlated with acceptance, and, e.g., a good mood or environmentally friendly behavior. For future success of NoMix-projects, we recommend authorities follow an integral strategy. Lay people will then find the NoMix-concept appealing and support this promising bathroom innovation.

Combining urine separation with waste design: an analysis using a stochastic model for urine production.

This paper explores the stochastic properties of human urine production in order to assess the potential of combining urine separation with waste design. The aim is to provide specific information about the dynamics of urine production at a microscopic level for the design and the control of the urine waste stream. Based on measured data a stochastic model is developed that is capable of providing stochastic information on the frequency, timing, and volume of urine releases into each single toilet in a catchment. It is then demonstrated in a virtual case study that the design of the human wastewater stream in terms of urine content can (1) reduce the ammonia peak loads at dry weather flow conditions by approx. 30% (which could effectively substitute the expansion of wastewater treatment plants) and (2) reduce the impact of combined sewer overflows on the aquatic environment. With respect to the latter a reduction of more than 50% is demonstrated in terms of annual urine volume released via the overflow.

Source separation and decentralization for wastewater management.

Is sewer-based wastewater treatment really the optimal technical solution in urban water management? This paradigm is increasingly being questioned. Growing water scarcity and the insight that water will be an important limiting factor for the quality of urban life are main drivers for new approaches in wastewater management. Source Separation and Decentralization for Wastewater Management sets up a comprehensive view of the resources involved in urban water management. It explores the potential of source separation and decentralization to provide viable alternatives to sewer-based urban water management. During the 1990s, several research groups started working on source-separating technologies for wastewater treatment. Source separation was not new, but had only been propagated as a cheap and environmentally friendly technology for the poor. The novelty was the discussion whether source separation could be a sustainable alternative to existing end-of-pipe systems, even in urban areas and industrialized countries. Since then, sustainable resource management and many different source-separating technologies have been investigated. The theoretical framework and also possible technologies have now developed to a more mature state. At the same time, many interesting technologies to process combined or concentrated wastewaters have evolved, which are equally suited for the treatment of source-separated domestic wastewater. The book presents a comprehensive view of the state of the art of source separation and decentralization. It discusses the technical possibilities and practical experience with source separation in different countries around the world. The area is in rapid development, but many of the fundamental insights presented in this book will stay valid. Source Separation and Decentralization for Wastewater Management is intended for all professionals and researchers interested in wastewater management, whether or not they are familiar with source separation. ISBN: 9781780401072 (eBook) ISBN: 9781843393481 (Print)

Effect of heterotrophic growth on nitritation/anammox in a single sequencing batch reactor

The combination of nitritation and autotrophic denitrification (anammox) in a single sequencing batch reactor (SBR) is an energy efficient process for nitrogen removal from high-strength ammonia wastewaters. So far, the process has been successfully applied to digester supernatant. However, the process could also be suitable to treat source-separated urine, which has very high ammonium and organic substrate concentrations (up to 8,200 gN/m3 and 10,000 gCOD/m3). In this study, reactor performance was tested for digester supernatant and diluted source-separated urine. Ammonium concentrations in both solutions were similar (between 611 and 642 gN/m3), thus reactor performance could be directly compared. Differences were mainly due to higher activity of heterotrophic bacteria in urine. Nitrogen removal was slightly higher for source-separated urine, because heterotrophic bacteria denitrified the nitrate that was produced by anammox bacteria. In spite of higher heterotrophic growth with source-separated urine, calculated sludge concentrations at steady state were higher with digester supernatant due to accumulation of inert particulate organic matter from the influent. Although the sludge concentrations are less problematic for source-separated urine, process instabilities are more likely, because lower pH values are reached and heterotrophic denitrification can cause sudden increases of nitrite concentrations and/or nitric oxide. Both compounds inhibit aerobic ammonium oxidizing bacteria, heterotrophic bacteria and, most importantly, anammox bacteria. Nitrite and nitric oxide production by heterotrophic denitrification must be better understood to optimize nitritation/anammox for source-separated urine.

Real-life efficiency of urine source separation

Urine source separation (NoMix technology) is a promising innovation in wastewater management. To improve and further develop NoMix technology, it has been implemented in four Swiss households and at our research institute (Eawag). We conducted measurements during one year on frequency of toilet usage (in households 5.2/person/day for weekdays, and 6.3/person/day for weekends), flushing behavior (30-85% small flushes), and recovered urine. We calculate the amount of urine effectively recovered per voiding in NoMix toilets (138 ml/flush in households; 309 ml/flush in womens toilets at Eawag), and waterfree urinals (225 ml/usage). We estimate urine recovery in the households to be maximally 70-75% of the expected quantity, leaving room for technical and behavioral improvements. Based on sampling of N and P concentrations, we suspect nitrogen losses in the extended urine piping system. For households and workplaces, the daily and weekly flushing pattern is recorded. Our results are in accordance with literature data from a shorter period but with more people. These results represent a good dimensioning basis for future urine source separation applications. An example of extrapolation to an entire watershed is presented. The flushing pattern corresponds well with the typical nitrogen loading of a treatment plant.