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Catalogue of Wastewater Management Solutions - Recirculation of Nutrients in Local Communities

Summary and conclusions

Ecological wastewater management is technically feasible, but requires much attention and effort by the users. Nutrients in wastewater and organic waste can be utilised, but this requires a special effort.

For some time, focus has been put on the possibilities of utilising nutrients from wastewater and organic waste from households as fertiliser in agriculture. Under the programme "Action plan for ecological urban renewal and wastewater treatment", a number of research and development programmes have been carried out on the consequences of handling domestic wastewater and organic waste based on ecological principles, including utilisation of nutrients.

This study summarises the latest experience from a number of methods aiming at increasing reuse of domestic wastewater and organic waste. In this project 12 systems are analysed. The 12 systems were recommended in a previous more theoretical study. None of the systems examined are ready for large-scale utilisation. However, several of the systems could in a relatively simple way be further developed to offer a good alternative to traditional systems. Generally, these systems require more attention and effort by the users than traditional systems, and it must be ensured that collected products can be utilised.

Background and purpose: From theoretical potential to assessment of feasibility

In a previous project under "Action plan for ecological urban renewal and wastewater treatment", a theoretical analysis of the potential for recirculation of nutrients from domestic waste and wastewater was carried out. The project recommended 12 solutions as the most suitable for increased recirculation of nutrients in different kinds of housing sectors.

Subsequently, studies of some of the components of the recommended solutions have been elaborated and building areas have been established where part of these solutions are used in practice. Thus, new knowledge has been obtained on the technical functioning of some of the solutions, i.e. urine separating toilets and biogas plants and experience from plants that have been operating for a reasonable period at a reasonably large scale. Furthermore, measurements and assessment have been made of hygienic and health aspects in connection with recirculation of nutrients via faeces and urine.

In general, recirculation of nutrients is characterised by pioneering and by decentralised and individual development in the private sector. Therefore, only limited documentation and publications are available from the implemented projects and tests. The material published on the experience of the users often gives a positive picture compared to the "official" studies.

The objective of this project is, on the basis of the experience gained during the last couple of years and from previous studies, to summarise information obtained and provide an overview of the most essential advantages and disadvantages of the individual solutions. This is meant as a help to municipalities, town planners, housing associations and interest groups who are considering the establishment of alternative handling of organic household waste and wastewater in preparation for recirculation of nutrients.

The Study: Summary of the experience from operation of selected systems for recirculation of nutrients

In this project 12 of the previously recommended solutions are evaluated, focusing on the practical viability, based on evaluation of the latest technical experience from the few locations with preliminary experience from operation of some of the components in the recommended solutions.

This report presents a catalogue of brief descriptions and evaluation of the proposed systems, supplemented with an overall description of the components included in the individual solutions. The catalogue is not exhaustive, but merely a practical guide to those considering one of the previously recommended solutions. Furthermore, the report gives an overview of locations in Northern Europe with large systems for ecological waste handling.

Main conclusions: The systems function in local communities with wide support, but are not ready for general utilisation in urban areas

Experience show that systems for wastewater and waste handling using recirculation of nutrients can function in local communities with wide support and understanding of the systems.

Most projects have been implemented based on a common ecological idea, thus most systems are operated and maintained voluntarily by persons with a special interest in this kind of waste handling.

Most of the systems cannot be considered as having been fully developed. The systems should be improved with regard to operation, maintenance, energy consumption, hygiene and comfort, before being applied in urban areas.

Compared to traditional wastewater handling, the solutions tested so far pose a far greater health risk due to the frequent and close contact with human waste products.

The total economy (socio-economic and locally) of the described solutions has not been analysed sufficiently to evaluate whether it is economically feasible to implement the described solutions rather than traditional solutions.

It should always be considered if other systems and application of waste products is more economically and ecologically feasible.

The following two systems are considered to be the most attractive and viable of the described solutions:

• Collection of urine for direct application as fertiliser in agriculture
• Collection of all solid fractions for biogas and application of the sludge in agriculture

The described solutions are most suitable for new building, since buildings as well as collection, treatment and disposal systems can be organised in a proper manner.

The current legislation gives a possibility for wide ecological application of waste products, with consideration of both health and environmental aspects.

Before implementation of large-scale systems, a number of specific studies should be conducted. Furthermore, the possibilities and barriers in connection with an extended use of recirculation of nutrients should be analysed. This analysis should also include an evaluation of socio-economy, sociological studies, theoretical market potential for the products and demands for the ultimate users, i.e. farmers, gardeners and the purchasers of their products, such as milk producers, food industry and individual consumers.

Project results

Some of the 12 systems are suitable for development whereas others cannot be recommended

12 specific solutions are described schematically, including experience from construction and operation, hygiene and health, energy consumption, recirculation potential, economy, area requirements, efforts required from citizens, and possibilities/barriers. This project concludes that:

• wet composting is not an attractive solution. Similar and more simple solutions exist which provide a better use of the waste products,
• local composting and application of faeces should not be applied in urban areas due to, amongst others, health risks and the present technological stage,
• collection of urine/traditional handling of the remaining waste provides increased recirculation with a simple/well-known system,
• biogasification of everything but grey water is most suitable for increased recirculation of nutrients and use of waste products as a resource.

Summarised evaluation of the actual technological stage

• All systems described include techniques and components that were neither fully developed nor sufficiently examined. These techniques and components should be developed to be more sturdy, reliable and maintainable.
• The systems with local handling of waste products are more sensitive towards undisciplined users, which might result in hygienic problems locally and complicate further processing.
• For part of the systems described, only limited experience is available from traditional residential areas. However, much experience is available on the use of the different components in ecological building areas and house sharing established by persons with a fundamental ecological attitude.
• Urine collection provides a great extent of recirculation of nutrients, and the process is technologically uncomplicated. The greatest problem is blocking and cleaning of valves and small tubes/pipes in the urine separating toilets and pipe systems for urine. The problem can be limited by regular caustic scrubbing, but could also be solved in another way, so that the system provides a level of comfort similar to that of traditional toilets.
• Composting toilets for faeces, if possible with addition of organic kitchen waste, have been dropped in urban areas, due to great difficulties in obtaining complete composting, difficulties in obtaining a texture of the end product, which is easy to handle, high energy consumption and different nuisances from smell and flies.
• The best application of waste products seems to be biogasification of kitchen wastes, faeces and urine, preferably together with other suitable materials. This uses the full recirculation potential for nutrients, and at the same time energy is extracted from the organic material. However, problems often arise from poor sorting of kitchen waste and economy of operation. If large volumes of urine are applied, the process can be hampered by the considerable extent of ammonium in the urine.
• Most systems imply more and closer contact with urine and faeces than traditional waste handling systems. This increases the health risk. Automation of the systems for collection, transport, treatment and disposal can limit the risk compared to the present manual handling of waste in systems which so far have not been tested.
• The systems described involve a certain transitional period and will for some time pose an increased health risk. It is estimated that after the transitional period there will still be an increased but limited health risk in changed handling, even if a number of precautions are followed.

Example of system which can be established at a larger scale after further development

One of the previously recommended systems is shown in figure 1. The system is based on collection and gasification of organic kitchen waste, urine and faeces, whereas grey water is disposed of by means of percolation or the like.

The advantage of this system is a very high degree of recirculation of nutrients combined with utilisation of the energy in the material without loss of nutrients. Compared to traditional systems, a large surplus of energy is obtained, partly due to fertiliser savings, and partly due to direct production of energy. Furthermore, the proposed collection method gives a substantial water saving.

Experience with certain parts of the proposed solution indicates that the following aspects should be improved: Joint collection of urine, faeces and kitchen waste will be more safe and sturdy if kitchen waste is collected separately and if vacuum toilets or water-free toilets are applied with collection of urine and faeces in a separate tank. The technological development of vacuum toilets is reasonable, but some improvement can be obtained. Correct sorting of kitchen waste must be secured in order to avoid problems with further treatment and disposal of the material.

Biogasification is a well-known and well-functioning technology, especially if the main product is slurry. Laboratory tests have shown that the process can also be applied for domestic waste products. It is, however, recommended to find an appropriate mixture and operation in the individual local communities. Biogas plants must be situated in a proper distance from houses.

The end product will be hygienised if the process takes place at an adequately high temperature. Furthermore, it should be ensured that the end product meets the requirements of the statutory order on application of sludge for agricultural purposes, and it should be secured that there are purchasers for the product, and analysed at what price the product can be sold.

Figure 1. Example of system being prepared for establishment in new housing areas in cities (N6)

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Version 1.0 Februar 2004, © Miljøstyrelsen.