Hassan I would suggest you consider some key application points first. Those answers and their suggested solution path would then characterize the value proposition you are looking to understand. So, depending where the application is would tell you it's value, which answers the feasibility question. As an example if you are considering the technology application for a rural area with no to marginal infrastructure for waste processing, then individual or small distributed simple process system(s) can have application, but very low value in terms of investment other than through NGO facilities. On the other hand if you consider application in a urban high-infrastructure environment, then you could look at integrated distributed systems that processes waste for energy, nutrient, water, and etc. since you would potentially have secondary markets for the byproducts. Now your value proposition changes into an investment strategy that can forecast value in services and products.
Be interested to know what direction you consider to take.
In principle, it is a good concept. However, you need to think about the methodology for collecting the emitted methane gas as well as it storage, Before you use this methane for heating purpose, the gas needs to be scrubbed and cleaned from other impurities.
In all, you need to be equipped with the right unit operations to obtain a continuous supply of methane from the sewage.
I suggest that you read papers about biogas (i.e., methane gas) production from the sludge in wastewater treatment plants.
of course it is feasible. You can generate power by producing bio gas from these household sewage. Then the bio gas can be utilized to produce electricity through generator. You can also use that bio gas for cooking purpose.