Noted for an array of services in the field of energy and water conservation solutions, we exclusively render Anaerobic Tank Designservices to our esteemed customers. With a perfect amalgamation of skilled technicians and supportive staff, we are able to offer impeccable services to all our clients at affordable prices. Anaerobic tanks are used for anaerobic digestion which helps to breakdown biodegradable material without the use of oxygen. Our engineers assist in Anaerobic Tank Design services based on the specific requirements of our clients. We ensure to offer top notch services to our customers within a stipulated time frame.
- Well experienced technicians render these services
- Timely completion of projects
- Reliable in nature
Anaerobic digestion in Anaerobic Tank Design Service
Biomass includes anything that is plant-derived; municipal solid waste, manure, crop residues, compost, food waste, paper and waste water. Crops can be grown specifically for use in Anaerobic digestion, as a supplementary feedstock, or a stabilising material. Biogas has been used in the UK since 1895 when gas from sewage was used in street lamps by the city of Exeter.
Looking at this in more detail, anaerobic digestion is a natural process where plant and animal materials are broken down by micro-organisms in the absence of air as follows:
- The Anaerobic digestion (in Anaerobic tank design service) process begins when biomass is put inside a sealed tank or digester
- Naturally occurring micro-organisms digest the biomass which releases a methane-rich gas, known as biogas that’s used to generate renewable heat and power. The process helps cut fossil fuel use and reduce greenhouse gas emissions
- The remaining material, known as digestate, is rich in nutrients and can be used as a fertiliser
Many forms of biomass are suitable for AD including food waste, slurry and manure, as well as crops and crop residues. However, woody biomass cannot be used because the micro-organisms can’t breakdown the lignin – the compound that gives wood its strength.
AD is not a new technology, it has been used in the UK since the late 1800s, but an increasing number of AD plants are being built to generate clean renewable energy. AD is also used to treat waste produced in homes, farms, supermarkets and industry which helps divert waste from landfill.
The products of AD are referred to as biogas and digestate. Biogas is a mixture of 60% methane, 40% carbon dioxide and traces of other contaminant gases. The exact composition of biogas depends on the type of feedstock being processed.
Biogas can be combusted to provide heat and/or electricity. Alternatively, the biogas can be upgraded to pure methane, often called biomethane, by removing other gases. This pure stream of biomethane can then be injected into the mains gas grid or used as road fuel.
Digestate is made from left-over indigestible material and dead micro-organisms. It contains valuable plant nutrients such as nitrogen and potassium. It can be used as a fertiliser and soil conditioner.
Different types of Anaerobic digestion
The term AD covers several different processes; the most common are shown below and can be classified according to whether they are:
- Mesophilic, 25-45°C; or thermophilic, 50-60°C
- Wet, 5-15% dry matter in the digester; or dry, over 15% dry matter in the digester
- Continuous flow or batch
- Single, double or multiple digesters
- Vertical tank or horizontal plug flow
Mesophilic or thermophilic
Mesophilic systems operate at 25-45°C while thermophilic systems operate at 50-60°C or above. Thermophilic systems have a faster throughput with more rapid biogas production per unit of feedstock and digester capacity and there is greater pathogen kill. However, the capital costs of thermophilic systems are far greater as more energy is needed to heat them and they generally require more management.
Wet or dry
The difference between what is considered a wet process and a dry process is quite small. Effectively, in wet AD the feedstock is pumped and stirred and in dry AD it can be stacked. Dry AD tends to be cheaper to run as there is less water to heat and greater gas production per unit feedstock. However, wet AD has a lower set-up capital cost.
Continuous or batch flow
Most digesters are continuous flow as opening the digester and restarting the system from cold every few weeks is a management challenge. They generally provide more biogas per unit feedstock and operating costs are lower. Some dry systems are batch flow and, to overcome peaks and troughs in gas production, multiple batch digesters with staggered changeover times are specified.
Single or multiple digesters
AD occurs in several stages; some systems have multiple digesters to ensure each stage is as efficient as possible. Multiple digesters can provide more biogas per unit feedstock but at higher capital and operating costs with a greater management requirement. Most digesters are single or double digesters.
Vertical or horizontal plug flow
Vertical tanks simply take feedstock through a pipe on one side of the tank whilst digestate flows out through a pipe on the other side. In horizontal plug-flow systems a more solid feedstock is used as a ‘plug’ that flows through a horizontal digester at the rate it is fed in.
Vertical tanks are simple and cheaper to operate, but the feedstock may not reside in the digester for the optimum period of time. Horizontal tanks are more expensive to build and operate but the feedstock will neither leave the digester too early nor remain within for an uneconomically long period.
The optimum system will be determined by what feedstocks are available, the output required, ie, energy production or waste mitigation, space and infrastructure.
Planning an Anaerobic digestion project
A typical AD project can be divided into three planning phases; design, build and operation. The first stage is to identify a suitable site and determine what the feedstock will be.
Upon choosing a site the following needs to be evaluated:
- Site layout and space to ensure sufficient space and access for construction, operation and storage
- Feedstock supplies and maintenance access
- Visual impact in terms of topography and natural screening
- Regulatory and environmental requirements regarding buildings and water course proximity
Planning permission is necessary for most anaerobic digestion installations. Small scale digesters using only on-farm waste may be passed as ‘Permitted development’, but local authorities must be consulted in the early stages of planning for confirmation.
Any installation accepting third party waste will need full planning permission.