Refugee permaculture = Awesome! Good for you!
Living, traveling and teaching permaculture in China for the past many years, I can say that the government subsidized humanure biogas digesters that everyone claims are so great here were a big flop. Farmers largely prefer to use raw humanure in their fields rather than to fuss over leaky, disgusting to clean, extremely low output energy systems. Do you have research showing the effluent is pathogen free and safe to use? I see the opposite.
http://www.sciencedirect.com/science/article/pii/S1438463914000388
At the very most, only faeces should be added to a digester, as urine will only force more putrid liquid effluent out of the system without adding any carbon to be transformed into biogas. Please don't be like most NGOs, mindlessly promoting sustainable tech without trying it first! A single digester takes an incredible amount of investment, labor, energy and non-recyclable materials to build compared to what most people get out of them before abandonment. One fast hot shower for 10 people's poo, half a truck of bricks and cement... Save the energy from the brick kiln and cement processing for the hot water. Better yet, use solar hot water!
Back to composting toilets:
Our team has some valuable experience designing and using group composting toilets in poor and developing regions. From our experience, a group use urine diverting composting toilet using sawdust will need about one large 360L (95 gallon) wheelie bin per month per 15 adults, and will fill a 5 gallon bucket of urine at least once per day.
It is my opinion that a non-removable container would mean building an unimaginable amount of separate toilet systems, even per 100 people. If I'm calculating correctly, that's roughly one cubic meter of waste storage, or one double chamber latrine per 3-4 people on a yearly cycle, not accounting for extra sawdust added to soak up urine. And although neither material is ideal, I just can't see how a cement box is an improvement over a HDPE bin in terms of Eco-friendly materials or safe waste handling practices. Surely a sturdy 360L bin has a higher reuse, resale or recycling value than a pile of broken cement blocks!
I suggest urine diversion, collection and use for everyone, at every deposit. Any urine included in sawdust composting system will require huge amounts of sawdust to soak up and equalize, where urine diversion can be easily utilized for planting crops, trees, etc. We use a simple urine diverting squat toilet already on the market here in China, and add a one way valve to the urine drain line to effectively seal the collection reservoir. We use a large urine storage reservoir, usually a 200L plastic barrel, to collect the urine and have it ready for mixing via a tap in the bottom of the barrel connected to an in-line irrigation source for convenient fertigation via hose. For men, a urinal connected directly to the barrel with the same one way valve reduces wait times on the toilet considerably. If tapeworm is a concern (typically the only urine-transmitted pathogen) a sealed barrel can be left for 30 days at >20C for sterilization, or longer at lower temperatures. If used by the same family to grow their personal plot, sterilization is typically irrelevant. When kept in a sealed container, smell is not an issue and the urine will keep ideal ratios of plant nutrients to grow almost anything, even a year later, and apparently contains nearly 80% of the plant nutrients in our waste stream. In that case, shouldn't it be considered a permaculture taboo to simply soak this stuff into the ground water, clearly a pollution concern, or to keep it in a latrine bin or straw bale, where much of the nutrient value can volatilize into the air?
We usually drill a small hole 10cm from the bottom of the rollie-bin for any needed drainage and added aeration and put bins in a shady spot to the side of the toilet for composting, then cover with old cloth to prevent sun damage and overheating in our subtropical climate. The actual contact with the waste is a bare minimum, and I usually feel comfortable removing bins without gloves, a vast improvement to the often disgusting composting toilet designs we have used in the past. Because we still add a healthy helping of sawdust after each use and exclude the urine, the process often starts with black soldier fly thoroughly breaking down and mixing the materials (1/3 reduction in volume in less than a month) and ends up as a fungal rich compost at six months to one year. We also suggest adding worms after the initial breakdown period to help with sterilization and improve compost quality. If bins are limited, they could be dumped after two or three months and left to finish composting near the garden or orchard for the additionally needed time. This could mean as little as a single toilet and 3 bins per 15 people for a permanent system. (As compared to 3 to 5 complete double chamber composting toilets for the same amount of people). Full 360L bins, composed mostly of sawdust, are not particularly difficult to move; an average 20 year old female is able to roll them across smooth, flat land without a problem. DO buy sturdy bins with large repairable wheels and a strong axel.
I can understand an emergency pit latrine, but if people are expected to be around for even two months, a urine diverting toilet will make it possible to sustainably grow many greens, etc. Plus, what an amazing opportunity to teach a group of people in need how to lose dependence on purchased fertilizers for sustenance agriculture, rather than how to effectively waste nutrients and pollute their new environment.