when operating batch mesophilic digesters fed with organic fraction of municipal solid waste (OF-MSW), with and without admixture of primary sludge (PS), noted that there was incomplete digestion in reactors fed solely on OF-MSW, and that it was relieved by the addition of PS but not of vitamins. The authors attributed this to the possibility of a shortage of macronutrients like nitrogen in DF-MSW which were compensated by the PS.