Composting is the controlled decomposition of raw organic material into biologically stable humic substances. This is carried out by micro organisms and invertebrates in the presence of oxygen. The final produced compost is stable, doesn't degrade further and is an excellent soil amendment. In fact, the use of compost as a soil amendment is so well established that it was first documented 2000 years ago. Following this module, you'll be able to explain co-composting treatment process and operation discuss operation and maintenance requirements and name design parameters. Since composting is so well established there's already a wealth of information available. If you want to know about the science operation, or technologies of composting I recommend watching the composting modules in the third week of our MOOC on municipal solid waste. You could also download the decentralized composting book from our website and also the international water management association or IWMI series on resource recovery and reuse, specifically volumes 2, 3 and 15. In this module, I will not focus on composing science I will focus on the factors that are specific to co-composting of fecal sludge, based on the operating experience of IMWI with co-composting in Ghana who helped me to prepare this module. So why do you need to co-compost? Why not just compost fecal sludge on it's own? The Carbon to Nitrogen or C to N ratio is too low in fecal sludge, so you need to mix it with carbon rich organic matter. For example, in Ghana the dewatered fecal sludge that IMWI is working with has a Carbon to Nitrogen ratio of 11 plus or minus 3. So input materials to compost actually need to have a C to N ratio between 25 to 1 and 35 to 1. Listed in this table for your reference are types of organic waste that you could use for co-composting depending on their availability, cost and qualities. Qualities such as moisture, carbon to nitrogen ratio and particle size. The qualities will also affect required composting times to achieve stabilization. For co-composting IWMI is using food waste with the Carbon to Nitrogen ratio of between twenty-eight and thirty-two to one and sawdust with the Carbon to Nitrogen ratio of about fifty. Another important operating consideration is that fecal sludge is mostly moisture and so it needs to be dewatered prior to co-composting for example, with drying beds. IMWI is starting with fecal sludge that is 93-99% water. Shown here is the sludge in Ghana just being loaded into drying beds. It's also important to consider the source of the fecal sludge. A sludge that is very fresh, with short storage times will not dewater as well for example public or commercial toilets. So then it needs to be mixed with more stable sludge that has a longer storage time. It also needs to be considered that the two different types of sludge will have different total solids concentrations. Following dewatering the sludge from these beds is 20-35% total solids or 65-80% moisture. In general, it is removed from drying beds when it is spadeable meaning that you can shovel it. The residents time on the drying beds depends on the climatic conditions and in Ghana varies between 7 to 21 days. The food or market waste also needs to be sorted to remove inorganic waste that you want to keep out of the compost. And in the case of IMWI, it also needs to be air dried for two days to reduce the moisture content from as high as 75% down to 50% or less. Sawdust on the other hand typically does not require drying. Compost feed in general needs to be around 50-60% moisture like a damp but not wet sponge. The next consideration for pre-treatment prior to the composting process is particle size. Feed stock that is too large will take too long to compost but if the pieces are too small it can also reduce pore space and oxygen transfer. Shown here is manually breaking up food waste prior to co-composting. If the dewatered fecal sludge is in large clumps it also needs to be broken down first. So now you're ready to build your own compost pile. Which technology will you use? Obviously prior to this step a decision would have to been made on technologies. Factors influence the decision of a technology include investment maintenance, space, time and labor, also volumes need to be considered. This decision matrix is covered in the solid waste management MOOC. Other important design factors include a roof to ensure the compost does not get too wet in the rainy season or dry out too fast in the sun. Prior to making your compost pile, you need to determine the correct ratio of fecal sludge and organic waste to end up with the proper moisture, Carbon to Nitrogen ratio and particle size for composting. In the case of IMWI, they are mixing 1500kg of organic waste to 500kg of dewatered fecal sludge to make a pile that's 2000kg. Alternatively, they measure by wheelbarrow, 48 wheelbarrow organic waste to 16 wheelbarrow of dewatered fecal sludge. These two streams are mixed together in a heap with around 13L of water, sprinkled in with the watering can and then it's all mixed together. Here's a heap that was made with market waste, sawdust and fecal sludge. During the processing you will need to control the temperature and moisture. This is done by turning, aeration, and adding moisture. pH also needs to be monitored as does temperature with time as an indicator of pathogen reduction. The temperature needs to be maintained at 50 degrees Celsius or higher for more than four weeks to achieve adequate pathogen reduction, which is especially important when composting the fecal sludge. However, you also do not want the pile to get too hot, because although heat kills pathogens it can also be bad for the organisms doing the composting. In IMWI's experience, 90-100% of helminth eggs are inactivated during an 80 day composting period. And for heap composting, stabilization takes two to four months depending on the feed stock. Depending on the technology and management, however the processing time varies and it could even be up to a year. Compost piles are turned by moving them from one place to another, to ensure that all parts are evenly treated. This is important for stabilization and also pathogen reduction. You see, this pile is still in the active phase and is steaming. Water is also added during the turning process. Prior to selecting composting as an option, it is important to evaluate the potential end users and the market demand, as it drives the continuity of the whole system. If it seems viable, then other factors to consider include waste volumes, availability, quality, economic viability, and local laws. This book, Marketing Compost, can also be downloaded from Sandec website. Depending on the market demand, one way to increase the market potential of compost is to create a product that is fortified with nutrients so that it is a fertilizer. In addition, because the compost is bulky transportation costs need to be considered. IMWI addresses this by creating pellets with added nutrients from the finished compost, that they call fortifier. In summary, variables that are required for designing a composting facility include waste streams, availabilities total volumes, total carbon and total nitrogen moisture particle size and porosity and markets. Important parameters for operation include temperature moisture turning aeration pH, and indicators for things, such as maturity and quality. In this module, we learned about co-composting treatment process and operation, design parameters and operations and maintained requirements. Important points to remember about co-composting include that with properly maintained temperature you can achieve pathogen reduction and stabilization. Dewatering the fecal sludge is mandatory prior to composting composting technologies are low cost, but also require space and the end product is a compost which has the same uses as any compost. Thank you for joining, see you next time.
