To divert from fossil fuels, nearly 20 k of biogas plants have been built in Europe over the past two decades. Although this trend is not closely followed in the rest of the world, it is still represented by other tens of thousands of installations. Since average biogas plant produces some 10 k tones of fermentation residues (hereinafter referred to as FR) annually, many managers and engineers are intensively looking for an economically efficient way to handle this waste. Under the new solution, FRs were pyrolyzed using waste heat from the biogas combustion engine. The obtained charred FRs (hereinafter as CFR) were incorporated in concrete at various dosages. It was revealed that up to a weight ratio of approximately 20%, concrete density decreases without its mechanical properties being degraded. Since the CFR are nowadays highly economical, the above-stated method represents an environmentally friendly and also financially promising solution that is, to our best of our knowledge, the most important contribution of this work.