The number one treatment objective in faecal sludge management is always protection of public health. Through protecting people from pathogens that make them sick. In this module we'll introduce you to two treatment technologies that can achieve high levels of pathogen inactivation: Ammonia and lime treatment. Following this module you will be able to explain how pathogen inactivation occurs in ammonia and lime treatment. Discuss operational maintenance requirements of these technologies. And considerations for their implementation. Ammonia treatment for pathogen inactivation faecal sludge is currently in the research and development phase. Ammonia treatment relies on the toxicity of ammonia to pathogens. Ammonia can be added to the faeces in the form of urea. But this treatment technology is really interesting because ammonia can also be provided through urea that is included in urine. Nitrogen urine is in the form of urea, but which is converted to ammonia by the urea's enzyme, that is available throughout the environment. Ammonium nitrogen and ammonia nitrogen are in equilibrium with each other. This graph shows the fraction of nitrogen that is available as ammonia as a function of pH and temperature. As shown in this graph, by increasing the pH for example by the addition of lime or ash, the ammonia nitrogen concentration can be increased. At a pH below 8.5 a mixture of urine and faeces will still have a lower ammonia concentration for pathogen inactivation. At this pH, most of the nitrogen is in the form of ammonia that is not harmful for pathogens. An increase in temperature also increase ammonia concentrations. Next to the toxicity of ammonia the high pH is also additional mechanism for pathogen inactivation in an ammonia treatment. Faecal sludge collected from septic tanks and pit latrines is mostly water, which dilutes the ammonia and results in low concentrations to be available for pathogen inactivation. Even at an elevated pH. Loss of ammonia and ammonium that are volatile to open manholes and septic tanks, or drop holes and pit latrines, also reduce the concentration of ammonia available for pathogen inactivation. In contrast to this type of sludge, high levels of pathogen inactivation could be feasible with faeces and urine when we lower the amount of flushing water and we are in sealed tanks. In laboratory experiments in Sweden at 20° C and a pH of 9, ammonia treatment could inactivate 99% of Ascaris eggs, which is the common Helminths egg in only 24 days. A decrease in a temperature and an increase in flush water, increase desaturation for the same level of pathogen inactivation from several weeks to several months. So moving from the laboratory, how could these results be used in practice? One attempt at the safe sludge project that is based on the collection of faeces and urine without any flush water. In the first step, faeces and urine are mixed together with the contact time of 4 hours, to convert urea with the enzyme urease into ammonium. Following, a material increasing the pH, which is lime and ash, is added which converts ammonium into ammonia. Then this is kept for hours or days for inactivation of pathogens. It is important to convert urea into ammonium before increasing the pH; as an increase in pH inhibits the enzyme urease. In the laboratory experiments in the United States, 99% of ascaris eggs were inactivated through this process. Such a treatment and process could be implemented for pathogen inactivation in innovative on-site sanitation technologies after treatment following separate collection of faeces and urine, As shown here with these jericans for urine collection, and a tank for storage, in Bolivia. Lime treatment, which is also called alkaline treatment, is a common treatment technology for waste water sludge. But also has been implemented full-scale for faecal sludge for example for the treatment of septic tank sludge in the United States or in the Philippines. Lime is a fine white powder. Based on available litterature on waste water sludge, the most common form of lime that is used in lime treatment is hydrated lime, or calcium hydroxide. In lime treatment, sufficient amount of lime are added to the faecal sludge to increase the pH to 12 for several hours to a month. Such a high pH slows down or stops biological processes that are responsive for odors and it inactivate pathogens. As discussed before for ammonia treatment, the increase in pH also results in the increase of ammonia concentrations that can contribute to further pathogen inactivation. Lime can be addible to liquid, sludge, and also sludge following the watering. Addition of lime to more liquid faecal sludge has the added benefit it could improve solid-liquid separation processes. During laboratory research that we conducted together with our research partners in Dakar, lime improved dewatering by 90-95% compared to an untreated control without lime. This can reduce the time and space required for dewatering, for example on unplanted drying beds. The dosage of lime to adequately raise the pH is an important design and operational parameter for lime treatment. The average dosage of several lime treatment applications in the United States with septic tank sludge, and also application in Philippines was 20% lime per dry mass of sludge. In one study in Blantyre, Malawi, addition to 20-35% lime per dry mass of sludge was successful in increasing the pH to 12. As lime is dosed as a function of total solids and they can be variable and also the chemical characteristics of sludge can be variable that influence lime treatment it is always important to determine the required dosage based on a local sludge characteristic. This can be done by a simple bench and pilot scale experiment where different amounts of lime are added to faecal sludge as shown here in the Philippines. Following mixing of the lime and the faecal sludge, the pH can be monitored over time with a handheld pH meter. This picture shows an example of lime treatment of a septic tank faecal sludge in the Philippines. The workers are adding lime in a mixing tank
The workers are adding lime
in a mixing tank to the faecal sludge in powder form, or a slurry prepared with water. Lime is highly corrosive for infrastructure and equipment and personal protective equipment such as safety goggles, boots, long-sleeve clothes and face masks should always be worn. This is because the same process that increase the pH in faecal sludge, also increase the pH most surface in humans, such as the skin, eyes and lungs. Following addition of lime, thorough mixing is required to ensure contact of faecal sludge with lime. As shown in this picture, this can be done manually, but mechanical mixing can be more effective and has the potential to produce higher pH values at the same lime dosage. So how effective is lime treatment in the inactivation of pathogens? In one study in Blantyre, and in another study in Phnom Penh, Cambodia, additional lime reduced E. coli concentrations below the limits recommended by the World Health Organization for use in agriculture. However, knowledge from lime treatment of waste water sludge suggests that because Helminth eggs are more persistent bacteria, treatment may require longer storage durations at a high pH. Also the effectiveness of a pathogen inactivation will depend on the type of the pathogen and the initial concentration of pathogens in a local context. It is always important to assess the inactivation of pathogens as a function of pH and time for the local context. Wrong assumptions can have a severe public health impact. Lime treatment has the benefit that is relatively quick, robust and effective for pathogen inactivation. It also has a small treatment footprint. All of these characteristics also make it suitable for emergency situations. However it is important to consider these benefits and balance them with the operating cost, which are mainly purchase of the lime. Price for lime can vary considerably between countries. For example, in the Philippines of price 150-100 dollars per tonne, in Senegal of 250 dollars per tonne, and in Malawi of 800 US dollars per tonne has been reported in the literature. Lime treatment inhibits biological process is harmful for the pathogens by increasing the pH. It is important to consider that this process can only be temporary and pathogen regrowth might occur if the pH drop below 11. For example during storage, transport, or use of the treatment product. Pathogen in incubation only remain safe at a pH of 12. Another important consideration, is that lime treatment does not reduce the sludge volume, as for example anaerobic digestion. In contrast, the addition of lime increase the mass of sludge that needs to be managed and disposed. It is also important to consider the characteristics of the sludge following lime treatment as it can influence subsequent treatment steps and resource recovery. Co-composting, for example, is based on microorganisms that inhibited the lime treatment and the high pH following lime treatment may not be beneficial for all soils. Lime is also inorganic and therefore doesn't contribute to the fuel value, which means that lime treatment uses the energy value for energy recover of solid fuels. In this module, we introduced lime and ammonia treatment, that are two technologies for pathogen inactivation. In both treatment technologies, the toxicity of ammonia nitrogen and a high pH are the main mechanisms for pathogen inactivation. The effect of these technologies for pathogen inactivation will depend on the type of concentration of pathogens the dosage of lime and ammonia required to produce environments that are toxic to pathogens, and the contact time. For long-term operations of these treatments it is important to consider that both technologies rely on reliable supply of ammonia in the form of urine urea and lime.
