Professor Petter D. Jenssen, Associate Professor Cassandra Bergstrøm and Professor Arild Vatn at the Norwegian University of Life Sciences examine the hidden value of the waste products we all produce
Think for a moment about human waste. Most of us think of excreta as something we need to get rid of. What if we think about it as a resource – a way to fertilise a vegetable garden, an orchard or provide part of the energy needs for heating and cooking?
This is not a far-fetched scenario, but highly realistic according to scientists at the Norwegian University of Life Sciences (UMB) in Norway, pioneers of environmentally safe solutions to organic waste and wastewater treatment.
Fertiliser for the world?
In developing countries, reuse of excreta can substitute 30-100 percent of current mineral fertiliser use. In developed countries the number is 15-20 percent, but can be increased through advances in agricultural practices. Our excreta is the source of about 90 percent of the nitrogen, phosphorus and potassium in wastewater.
These are the three major nutrients needed for plant growth. While they can be a resource in agriculture, they are currently pollutants in our waters. Thus recycling our waste provides a win-win situation of fertilising our agricultural soils and keeping rivers, lakes and seas clean.
At present China and Morocco have most of the remaining mineral phosphorus reserves. China, having evaluated their national situation, are ceasing their export. The European Fertiliser Manufacturers Association predicts demand to exceed production in the year 2040. Arno Rosemarin of the Stockholm Environment Institute envisions serious phosphorus shortages and escalating food prices within one to two decades.
As a consequence the Swedish government is the first country so far to decide to recycle 60 percent of the phosphorus from sewage by the year 2015.
Urine makes the difference
It takes 38MJ of electric energy to produce 1kg of nitrogen fertiliser. Every kilogram of nitrogen fertiliser we spread is equivalent to the energy in one litre of diesel oil. Trials show that yields comparable to mineral fertiliser can be obtained using urine. Urine contains high amounts of nitrogen that naturally converts from the excreted urea to plant-available ammonia during the six months storage required by the WHO guidelines for “Reuse of Excreta and Greywater in Agriculture” to sanitise it. Urine also contains phosphorus and potassium and thus constitutes a nutrient source that is available wherever people live. In Bangalore, India, urine collected from 700-800 slum-dwellers fertilises banana fields producing 50 tons of fruit per year.
How can we collect the urine? A modern urine-diverting toilet is needed to separate and funnel the urine to a storage tank. Urine diverting toilets can easily be retrofitted in any building. Together with waterless urinals, such as those that are currently used with excellent results at the UMB, large∞scale urine collection is possible. The urine can be collected by local farmers or used in your own garden after appropriate storage. Collection of urine in urban areas challenges the downstream handling system. For extensive use of large volumes dewatering or solidification is necessary.
Further challenges arise because medicinal residues are mainly excreted in the urine. Modern wastewater treatment plants do not remove pharmaceuticals efficiently, thus collection of urine would protect waters from these chemicals that are shown to have negative effects on aquatic biota. Soil has more potential to degrade pharmaceuticals than aquatic environments and provides a better option for final disposal. But the breakdown and potential assimilation of such chemicals in agro-ecosystems needs further study.
Another idea arises from the recognition that urine can be an important nutrient source for second-generation biodiesel production. At UMB, algae fed with urine have been shown to produce as much fatty acid and subsequent biodiesel as algae fed with mineral fertiliser.
Black water recycling
In 1997 a first-generation recycling system, based on separate treatment of black water (urine and faeces) and water from kitchen, shower and washing (grey water), was built to serve 48 students at the UMB student dormitories. The system uses a modern and comfortable vacuum toilet system.
This system reduces water consumption by 30 percent, it nearly eliminates pollution and produces a valuable plant fertiliser and soil amendment product from the waste material. A liquid-composting reactor is used to sanitise the black water and runs with a net energy surplus in terms of heat. Today the scientists at UMB are pursuing anaerobic treatment for production of biogas from black water and other organic waste. Biogas has a higher energy quality than heat and can be used for cogeneration of heat and power or to power vehicles. Acknowledging the scientists’ activities, the university board decided to convert the entire UMB into a zero emission university and in 2008 the first building was retrofitted with vacuum toilets.
Eliminate secondary sewers?
In Oslo, the capital of Norway, a grey water treatment system serves 100 habitants of a low energy apartment building. The treatment system utilises technology developed at UMB and has produced an effluent that meets the European bathing water standards since its opening day in the year 2000. The effluent is suited for local discharge, irrigation or groundwater recharge. With such decentralised grey water treatment units and separate collection of the excreta, secondary sewers that constitute the most expensive part of a sewer system can to a large extent, be eliminated. As a consequence, more funds can be invested in treatment and recycling without increasing the total cost.
Appropriate sanitation for all
Our excreta is the main source of pathogens in wastewater. Open defecation and discharge of untreated wastewater into gutters, storm-drains or nearby streams introduce substantial amounts of pathogens into watercourses and wells. This is responsible for waterborne diseases killing more than three million people every year and reducing the quality of life for many more millions.
Nearly half the world population lack access to appropriate sanitation (i.e. an improved pit latrine is regarded as appropriate). The internationally agreed Millennium Development Goal for sanitation intends to halve the number of people without access to appropriate sanitation by the year 2015. With the current rate of progress, it is estimated that we will miss the goal by 700 million people. This will leave 2.4 billion people without proper sanitation in 2015. Moreover 1.2 billion people, primarily in rural areas, will still have to practice open defecation.
Can we meet the need for sanitation by providing traditional flush toilets and sewers to the world? The answer is no. In many areas there is not enough water to sustain traditional toilets, not enough money to build sewers and treatment works, and not enough competence and interest to maintain such systems.
There are close links between unclean water, inadequate sewage treatment, malnutrition, poverty and premature death as well as low productivity in farming. If we are to deal with these vital issues touching at the heart of humanity and human rights there is a clear need for innovation as well as information and capacity building to implement sanitary systems to meet local needs.
Engineering programmes in water and sanitation focus on the design of sustainable systems to suit local conditions. A new international MSc programme; “Sustainable Water and Sanitation” developed in cooperation with universities in Nepal and Pakistan, target health and development in addition to decentralised, natural and source separating sanitary systems. Thus the students learn about a wide range of technical options in addition to traditional centralised sanitation. They learn about health challenges and risks. And, they are trained to engage all relevant stakeholders, consider local cultural and political contexts and overcome obstacles of inadequate institutional structures.