A bacteria growth device (1) for use with bacteria in a substantially liquid medium, the device (1) comprising at least one strip (5) having a surface area shaped and sized for receiving bacteria present in the substantially liquid medium and for allowing attachment of said bacteria onto the surface area of the at least one strip (5) so as to promote growth of the attached bacteria. The substantially liquid medium may be enclosed in a n aerobic environment, in which case the device (1) is used to promote the growth of aerobic bacteria. Alternatively, the substantially liquid medium may be enclosed in an anaerobic and/or anoxic environment, in which case the device (1) is used to promote the growth of corresponding anaerobic and/or anoxic bacteria. Also, described are an assembly including the above-mentioned device and the method associated thereto. Typically, these are used for promoting growth of bacteria destined for treating and purifying wastewater effluents which are high in biochemical demand, such as the wastewater discharges of residential and/or industrial septic/wastewater tanks for example.