Producing energy from wet waste

From the advantages of using a wet process for the creation of biogas to a real-life case of producing energy from domestic waste

The production of biogas using a wet process has increased significantly in Italy in recent years; in fact, over a thousand plants have been built based around this low-cost technology with highly flexible processes. Those investing in such infrastructures can enjoy numerous advantages:

The environment is ideal for the homogeneous proliferation of microorganisms, which means that any samples of the digester’s biological conditions are highly representative.
The volume is optimal for each specific fuel mix.
The entire volume of biomass in wet systems decomposes in an anaerobic environment, ensuring maximum efficiency. This is not the case in dry systems, where wood or other structuring material is required.
The quality of the digestate is much higher, thanks in part to the fact that incoming waste is pre-treated.

In general, it can be said that these systems ensure lower management costs while at the same time minimising operating costs. They are stable systems that produce high-quality compost, which must nonetheless be subjected to a precise protocol to establish its benchmark characteristics.

The lana biogas plant that produces energy from domestic waste

In 2006, a medium-sized plant opened its doors in the municipality of Lana. This plant makes use of the waste separation systems of over thirty cities to produce energy by means of a wet anaerobic digestion process. The incoming waste is first ground up and homogenised before being mixed with 7 tons of water, reducing the percentage of dry matter down to 4%. Subsequently, the solution thus obtained is passed through a grid that separates heavy materials from light ones, allowing the various impurities to be isolated.

Afterwards, the mass is channelled into a thickener, where the dry matter level reaches 11%. At this point the mass is ready for fermentation and is therefore sent to a digester, where it remains for at least 16 days at a temperature of 37 degrees Celsius.

The digestion process takes place at this temperature, leading to the formation of biogas consisting of 60% methane, which is burned in two co-generators with 334 kW and 536 kW of electric power.