Climate Change

The greenhouse effect is the phenomenon where the presence of so-called greenhouse gases leads to a warming of the earth's surface: Greenhouse gases allow solar radiation to enter the earth's atmosphere but prevent heat from escaping back to space. They absorb infrared radiation and reflect it to the earth's surface leading to a warming there. Many human activities cause greenhouse gas emissions which drive the anthropogenic greenhouse effect. According to the Intergovernmental Panel on Climate Change the atmospheric greenhouse effect will cause a rise in the mean global temperature of between 1.1 and 6.4°C by the end of the 21st century (IPCC 2007a), a change in rainfall patterns, a rising sea level and a weakening of sea currents which will have an additional impact on the global temperature distribution. In order to limit climate change to tolerable levels, global temperature rise has to be limited to 2°C (IPCC 2007b). To achieve this, greenhouse gas emissions would have to be reduced by 50% by 2050 compared to the level in 1990 (IPCC 2007c).

In the field of sanitation, the following greenhouse gases are climate relevant:

• Carbon dioxide (CO₂)is produced as a result of any fossil or non-renewable wooden biomass combustion. Similarly, the removal of organics and nutrients in wastewater treatment plants requires energy. The same holds true for the production of mineral fertilisers which is a very energy intensive process. Both the removal and the new production of nutrients for fertilisers require the consumption of fossil fuels leading directly to climate relevant CO₂ emissions. For climate protection, it is important to reduce fossil or non-renewable wooden biomass consumption.
• Methane (CH₄) is a potent greenhouse gas with a global warming potential 21 times higher than that of CO₂. In anaerobic processes, organic matter contained in domestic waste and wastewater is decomposed and biogas is formed which contains 60-70% methane. In soak pits, anaerobic ponds, septic tanks and other anaerobic treatment systems where biogas is either not collected or leaking (e.g. many UASB reactors), or even at the discharge of untreated wastewater into water bodies, anaerobic processes take place to different extents and methane is released to the atmosphere. For climate protection, wherever biogas is produced, it should be captured through a controlled anaerobic treatment and used as a renewable energy source. If the biogas cannot be used, then it has to be flared. As an alternative to a controlled anaerobic treatment, methane formation should be avoided through a low-energy aerobic treatment (e.g. dehydration, composting, constructed wetland).
• Nitrous oxide (N₂O) is the most harmful greenhouse gas with a global warming potential 310 times higher than that of CO₂. Nitrous oxide emissions occur during the denitrification process in wastewater treatment, at the disposal of nitrogenous wastewater into aquatic systems and also during mineral nitrogen fertiliser production. For climate protection, nitrogen should be recovered and reused as a fertiliser, or nitrogenous wastewater should be treated for the intended use and reused (e.g. for irrigation or groundwater recharge).

By using appropriate reuse-oriented sanitation systems with energy, nutrient or wastewater recovery and reuse, anthropogenic greenhouse gas emissions can be reduced (mitigation) as well as people's capacity to cope with climate change impacts can be increased (adaptation). In the field of sanitation, possible measures to mitigate or adapt to climate change impacts are described in the following sections about mitigation measures and adaptation measures.

Besides the avoidance of energy intensive aerobic treatment systems, sanitation systems can be operated in a way to produce renewable energy in the forms of either biogas or biomass and thus reduce the primary energy consumption:

1. Biogas production or its avoidance (see below and section about biogas production).
2. Biomass production (see section about biomass production).

Wherever biogas is produced, it must be captured and preferably used either for simple heat generation or for a combined heat and electricity generation, e.g. by means of a combined heat and power plant (see pictures below) or by a fuel cell. This can substitute the use of fossil or non-renewable energy sources. If the biogas cannot be used, then it has to be flared (this converts methane to carbon dioxide which has a 21 times lower greenhouse gas potential than methane, see section about relevant greenhouse gases). This results in the following recommendations:

• Where treatment size allows for it, replace existing (facultative) anaerobic ponds (also called "lagoons") and septic tanks by a controlled anaerobic treatment systems (e.g. biogas plant, UASB reactors, anaerobic baffled reactor).
• Design and build any new anaerobic treatment system as a closed gastight construction with biogas capture.
• Close existing open septic tanks as well as leaky biogas plants (e.g. anaerobic digesters, biogas settlers, UASB reactors , anaerobic baffled reactors, etc.) gastight and avoid venting by restoring the flares.

If neither the use nor the flare can be realised, uncontrolled biogas production should be avoided. Therefore, where septic tanks or biogas settlers are too small for a controlled anaerobic treatment (i.e. generally household level), aim at replacing septic tanks by appropriate, low-energy, (partially) aerobic treatment methods (e.g. dehydration, composting, constructed wetland).

Another possible measure is the heat recovery from:

• wastewater (e.g. from greywater or wastewater running in sewers or from the effluent of wastewater treatment plants) and its use.
• the heated pressurised air for the aeration of activated sludge tanks and its use.

Since these measures represent very local options for conventional centralised systems, they are not further discussed here.

The macro nutrients nitrogen (N), phosphorus (P) and potassium (K) contained in human and animal excreta can be locally recovered and safely used as fertiliser in agriculture (see also nutrient requirements of plants). In this way, they can substitute the energy intensive production of manufactured mineral fertilisers and their transport over long distances. Since N-fertilisers require more energy (REMY et al. 2006) and are consumed in larger amounts than P- and K-fertilisers (GELLINGS & PARMENTER 2004), it is sufficient to focus on nitrogen fertilisers only when considering energy demand and climate-relevant effects from fertilisers. Since 87% of the excreted nitrogen is contained in urine, from a climate protection point of view, concentrating on the recovery and reuse of the nitrogen contained in urine represents the most efficient means of emission reduction through nutrient recovery (see also urine fertilisation at small or large scale).

Therefore, artificial mineral fertilisers should be replaced by natural fertilisers (urine, sludge, dried faeces) as far as possible (see recharge and reuse for more information).

In order to adapt to water scarcity, the following measures should be taken into account (list is not exhaustive):

• Wastewater (esp. greywater), treated to the appropriate degree for the intended use ("reclaimed water"), or rainwater can be reused for the irrigation of food crops or lawns, or energy crops (see short rotation plantations or fertigation), parks and other public spaces, for groundwater recharge or as service water. In cases where potable water is used for irrigation, the use of treated wastewater substitutes the extraction, processing and distribution of potable water and thus may lead to energy savings. The main benefit however would lie in a reduced primary water resources demand. The nutrient content of the wastewater also reduces the need for mineral fertiliser input as mentioned. Further information on wastewater reuse in agriculture can be found in (WHO 2006).
• Reduce physical water losses through both the repair of leaking pipes and the introduction of a water pressure management of water pipe networks (see leakage control).
• Minimise virtual water losses by reducing the exportation of highly water consuming products (e.g. animal meat, cotton, rice) and increase the import of highly water consuming products (e.g. cereals) (see virtual water).
• Use dry toilet systems (especially in water scarce areas) for substituting waterborne sanitation systems. Toilets which don't require water for flushing, but can nevertheless be indoors (e.g. UDDTs, composting toilets), may save about 40 L/(cap · d) compared to conventional flush toilets.
• Install water collection and storage units (cisterns and underground reservoirs) providing water for drought periods (in regions with an intermittent water supply)
• Increase the cultivation of drought resistant crops.
• The irrigation methods used should minimise water losses through evaporation and infiltration (e.g. sub-surface irrigation).
• Seawater desalination plants might be installed if operated by renewable energies (e.g. Saharan solar power plants).
• See also optimisation of water use  for further information.
• In order to adapt to flooding, one effective measure consists of building sanitation system components in a way that they are either not affected by flooding (UDDTs built high enough above ground) or that water can evacuate quickly (elevated sludge drying beds, constructed wetland).

The Kyoto Protocol – the internationally binding contract on climate protection measures valid until the end of 2012 – assigns each participant country which has emission reduction commitments an allowed amount of greenhouse gas emissions. In order to reach this emission target at the least macro economic costs, the Kyoto Protocol offers three market-based flexible mechanisms. One of them, the Clean Development Mechanism (CDM), is designed for trading emission reductions which have been achieved in developing countries.

The CDM can be used for emission reductions achieved through sustainable sanitation systems. It can contribute to an additional financial benefit but also generates CDM-related costs which are mostly fixed and which compensate achieved credits to some extent.

Hence, for sustainable sanitation systems, a minimum project scale is required to make CDM economically attractive. This is very much dependent on both the baseline and the project scenario, the energy demand of the fertiliser production plants, the energy mix of the country considered, the transaction costs and the price of the carbon credits.

Assuming average transaction costs and a long-term price of 20 €/CER, the minimum project scale was found in (OLT 2008) to be around 25 000 PE1 (for energy recovery) and 37 000 PE (for nutrient recovery). The minimum project scale for an economic use of CDM for energy recovery (biogas use) and nutrient recovery (urine use) was analysed for a case study in India (OLT 2008). From an emission reduction point of view, this project faced favourable conditions in view of energy recovery and unfavourable conditions in view of nutrient recovery. Therefore the above indicated project scale for energy recovery represents an absolute minimum value, while the value for nutrient recovery can also be lower.

In order to reach this number, similar CDM projects may be bundled to a "Programme of Activities" (PoA). A manual for biogas plants at household level is given in (GFA 2009). Further information on PoA is available at (UNFCCC 2009).

Biogas production: Biogas is a renewable energy that can be used for cooking, lighting, heating purposes, and for generating electrical power. It is produced by bacteria that decompose organic matter under anaerobic conditions (i.e. in the absence of oxygen). The technology of anaerobic digestion has been applied to human and animal excreta for over 150 years. The anaerobic bacteria grow slowly and higher temperatures result in faster decomposition rates. For biogas generation various substrates can be used (often in combination of each other), e.g.

• blackwater, i.e. mixture of excreta and flushing water (best from low-flush or vacuum toilets)
• organic waste from households or agricultural farms
• animal manure
• sewage sludge originating from domestic wastewater
• human excreta from dry toilets

In many Asian countries, e.g. China, human excreta or so called "night soil" is being treated in this way together with animal manure and other organic waste. As a result of a Chinese national programme in the 1970s ("Biogas for every household"), the increasing energy demand and continuing efforts to combat wood cutting, there is an on-going interest in biogas which is supported by the Ministry of Agriculture. Today, there are five million family-sized plants in operation (BALASUBRAMANIYAM et al. 2008).

Biomass Production: Biomass is a non-fossil energy source which is neither always harmful nor always neutral to the climate. According to the UNFCCC definition (UNFCCC 2006), renewable biomass is understood as:

• wood (provided that wood harvest does not exceed its growth)
• other wooden biomass (provided that the cultivated area remains constant)
• animal or human manure
• solid organic waste (domestic or industrial)

Both food and biomass production are essential for people's livelihoods, and often compete with each other for available land, water and nutrient resources. Food and biomass production might be seen as equally important in economically rich countries with a safe food supply. But in many developing countries food production takes priority, whilst at the same time most people are dependent on biomass (particularly wood) for their energy supply, primarily to cook their food. One way to establish whether priorities should tend towards either food or biomass production is to carry out a national food balance taking into account food production and food consumption (OECD-FAO 2008). This can then be used as a basis for making decisions regarding the cultivation of more food or more energy crops. The use of sanitation-derived fertilisers in agriculture may increase the productivity of the land and thus decrease the conflict between food and biomass production at the local level (see also short rotation plantations).

It has been shown that sustainable sanitation projects can contribute to both mitigate climate change (through energy or nutrient recovery) and to adapt to climate change (through an intelligent water and wastewater management). Measures of energy recovery (or: renewable energy production) consist basically of either biogas or biomass production while measures of nutrient recovery are primarily based on nitrogen reuse. Water and wastewater management measures aim at coping with either water scarcity or flooding.

Most of these measures lead to greenhouse gas emission reductions. In case they were achieved in developing countries, they can be sold on international emission allowances markets and thus contribute to an additional financial benefit. In order to be financially viable, a certain minimal project size must be realise.