For fluidized bed systems, a critical R&D pathway toward sustainable distributed treatment is to simultaneously improve encapsulant longevity and the bioreactivity of encapsulated acetoclastic methanogens (Figure , F). When both bead lifetime is short (e.g., < 5 years) and 𝑘 𝑎𝑐 is small (e.g., < 6 CO •CO - Compared to fluidized beds, R&D of packed bed systems should prioritize increasing bead longevity over any other technological parameters because it dictates the frontier of system sustainability (Figure ). Both LC and CI can be significantly reduced by increasing the bead lifetime from 1 year to 3 years. Longer bead lifetime also allows the system to target a higher COD removal percentage by designing a larger packed bed reactor (i.e., optimal HRT increases from approximately 6.5 hours to 14 hours, Figure ). Although PEG hydrogel had been estimated to have a lifetime over 10 years in the literature, it was found in preliminary experiments that the addition of microbial cells and mixing high strength wastewater in the reactor could affect the structural integrity of the beads and significantly reduce lifetime to as short as 30 days. If the goal of the system is carbon neutrality (i.e., CI = 0 kg CO2eq packed bed reactor would require the beads to last at least 11 years without replacement, but the required bead longevity can be as short as 2 years with fluidized beds. Lower bed voidage (i.e., gray contour lines in Figure ) would make it even more difficult to achieve carbon neutrality.