Photo: Kai Pfaffenbach/Reuters

SaniGas - Energy from biological waste
Design by Constantin Boes.

The project is being developed within the framework of a disaster scenario. The focus is on energy generation in regions and situations where a stable supply through the public power grid cannot be guaranteed, but several hundred people have to be supplied. The planned application refers to the use in refugee or emergency shelters with a population of about 250 people.

Photo: Alvaro Fuente/NurPhoto/Getty Images

Research and problem statement
One of the most fundamental problems in the construction of refugee camps or sheltercities in open or isolated areas is the supply of energy and electricity. In most cases this is ensured by a network of diesel generators and in a few cases by solar energy. However, the systems are inefficient, the fuel either expensive or not always accessible and the power grid breaks down sometimes. Particularly in our networked society, where information is one of the most important goods, a stable power grid should be guaranteed as the basis for radio and internet supply. Particular attention must be paid to the strength of the frames and corners of the modules when designing and designing the system, as transport, weather and general use place heavy demands on the individual components. For easier storage and smooth loading and transport of the modules, the design is based on standardized Euro pallets. The sanitary facilities and the combined heat and power unit (CHP) each have the layout of a Euro pallet (120cmx80cm). The floor plan of the gas storage corresponds to four Euro pallets. The material must be rustproof and unbreakable in order to guarantee perfect use.
Functionality and processes
The system consists of 3 module units: The toilet cabins, the fermenter/gas storage and the CHP. All modules have a Euro pallet as a basic unit and can therefore be fitted to all conventional trucks, trailers or shipping containers. 
The usage process starts with the use of the toilet, which is a waterless system due to its individual sealing in fermentable bags. Once the business has been completed, the „flush“ is triggered and the excrements are placed in a bag produced from corn starch, which can be decomposed without leaving any residue, sealed and collected in a collecting container underneath the toilets. When this is full, the filled bags are placed in module two, where they are fermented at an operating temperature of 30-40°C and the gases are extracted to be stored in a gas storage tank for further use. 
The biogas produced by anaerobic fermentation has a methane content of 60-70% and can therefore be used as fuel for the combined heat and power plant.
The produced energy is then delivered to the residents and the rest of the system in the form of electricity or used as thermal energy for heating.
For a better general understanding of the module system, graphics have been created that explain the structure and function of the system. 
Sketches and modelling
In the process of form finding, various drawings, preliminary models and first 3D models were produced on the basis of the existing research. The CAD programs Autodesk Inventor and Rhino were used for this.
Model making​​​​​​​
In model making the details were concentrated on the toilet cabins. The other two modules are only shown as white models to show the proportions. The materials used for the models are a combination of acrylic glass and ureol. Parts from CNC milling, turned parts and lasered acrylic glass elements were used for production.
Module 1: The toilet cabie
The first module of the system is the toilet cabin. The double cabin is the heart of the system and the main interface with the user. 
On the outside, it defines the design language of the individual modules, with large radii on the outer shell and small radii on handles and doors. The orange „bumper“ protects the cabin from transport damage and is made of aluminium. It is visible from a distance and detaches itself from the mostly miserable surroundings of the camps. The cabin is entered through a swing door whose surface is illuminated by a homogeneous LED panel. This shows the way at night and illuminates the area in front of the toilets, which is intended to counteract abuse and harassment, which often occurs in refugee camps on or near the toilets. In addition, the panel illuminates the interior of the cabin and bathes it in a pleasant warm light that harmonises well with the curves of the interior.
The main task of the toilets is to provide hygienic, modern and robust sanitary facilities. In addition, the excreta is sealed in fermentable bags made of a corn starch polymer after the toilet visit. These are then further processed in Module 2.
Module 2: The fermenter/gas storage tank​​​​​​​
The collecting container with about 100 bags is pushed into the fermenter via a 3m long rail and tilted into a collecting tray in the control unit. There the bags are shredded to be fermented faster and fermentation begins. 
The biomass is permanently moved by a rake, which accelerates fermentation. 
The degradation of the organic matter in the fermenter takes place under anaerobic conditions (without oxygen):
Hydrolysis: In a first step, enzymes decompose the polymer macromolecules (carbohydrates, fats, proteins) of the biomass. The enzymes involved are amylase, protease and lipase. In this case, they act as exoenzymes outside the microorganisms. Carbohydrates are split into oligo- and monosaccharides. Proteins are broken down into peptides and amino acids and fats are divided into their individual components (fatty acids, glycerin).
Acidogenesis: Further degradation of the shorter compounds formed during hydrolysis to organic acids (mainly carboxylic acids) and alcohols. This produces substances such as butyric, propionic and acetic acids, but also substances undesirable for the quality of the biogas such as hydrogen sulphide and ammonia (mainly due to the nitrogen of the proteins).
Acetogenesis: The substances produced by hydrolysis and acidogenesis are degraded by microorganisms to acetic acid and its dissolved salt (acetate). Due to the disappearing alcohols and further increase in acids, the pH value drops.
Methanogenesis: Methane is formed in two different ways. First (A) from acetic acid, which is broken down into methane by methanogenic bacteria. Second (B), methane and water are formed from elemental hydrogen and CO2.

(A) CH3COOH -> CO2 + CH4
(B) CO2 + 4H2 -> CH4 + 2H2O

The biocoenosis of microorganisms that decompose biomass and produce methane in particular works best under anaerobic conditions. Another important factor for the activity of the bacteria is the temperature in the fermenter. There are different possibilities of plant management (mesophilic, thermophilic, hyperthermophilic), whereby the temperature should not exceed 75°C. The temperature in the fermenter should not exceed 75°C.
The species composition in the fermenter results mainly from the temperature, the pH value, the oxygen content and of course the input material (and thus the biomass composition). During the first 3 decomposition stages the following bacterial families are active: actinomycetes, micrococci, nocardias and corynebacteria. During methanogenesis, the activity of methanobacteria leads to the production of the desired methane content in biogas.
The resulting biogas is passed on via gas pipes to Module 3, which further processes the gas.
Module 3: The combined heat and power unit (CHP)​​​​​​​
The CHP is a building type of the class Mini CHP. This has an electrical power of 30 to 50kw and can be fed with various energy sources. Most efficient, however, is natural gas, the origin of which usually causes environmental damage, as it has to be born deep into the earth to produce the gas. The use of biogas is much more environmentally friendly and almost as efficient. In its normal use as a power plant for multi-family houses and public facilities, the CHP is operated with biogas containing 95-98% biomethane. In the CHP, which is used for the SaniGas system, only biogas with a content of approximately 70% can be used, since no higher concentration is possible in the gas due to the accelerated fermentation process. 
In the combined heat and power plant, the biogas is converted into electrical energy and forced thermal energy by combined heat and power generation. The latter is either used to heat public places, such as the hospital ward, or is further converted into electrical energy. This can then be used by residents to charge their mobile phones, laptops, radios and other electronic devices.
Back to Top