NOVELTY - Preparing sludge cake (I), comprises: fermenting liquid sludge at a temperature in the mesophilic temperature range for a pre-determined period to produce volatile fatty acids; maintaining the fermented sludge for a pre-determined period in the thermophilic temperature range to destroy any Escherichia coli reactivation or re-growth potential; digesting the pre-treated sludge in a digester to produce biogas with high methane content; and dewatering the digested sludge to yield the sludge cake.    USE - The process is useful for preparing sludge cake, which is useful in agriculture as the soil conditioner or fertilizer (claimed).    ADVANTAGE - The process is stable. The process recovers the energy content as biogas and reduces the odor and pathogen level of (I), thus enables it suitable for agricultural recycling. The process is simple to implement, and can be integrated easily and readily. The process provides sludge cake product, which is not susceptible to pathogen reactivation or re-growth. The digestion process reduces the solid content by about one third. (I) is stackable, easy to stockpile and can be transported. (I) is free of Salmonella. The process destroys Escherichia coli efficiently with much shorter contact times. The process reduces the Escherichia coli content by at least 99.9999%, thus (I) has less than 1000Escherichia coli count/g dry solid. The ability to determine Escherichia coli reduction was tested using biological assay. The result showed that the content of Escherichia coli were reduced from 20181818 most probable numbers/g (day 0) to 0 (day 3).    DETAILED DESCRIPTION - Preparing sludge cake (I), comprises: fermenting liquid sludge at a temperature in the mesophilic temperature range for a pre-determined period to produce volatile fatty acids; maintaining the fermented sludge for a pre-determined period in the thermophilic temperature range to destroy any Escherichia coli reactivation or re-growth potential; digesting the pre-treated sludge in a digester to produce biogas with high methane content; and dewatering the digested sludge to yield the sludge cake, where the sludge cake comprises a class A biosolids product as defined in US EPA 503 regulation or the enhanced treated standard as defined by the UK safe sludge matrix for use in agriculture as a soil conditioner or fertilizer containing at least 20 wt./vol.% solids. An INDEPENDENT CLAIM is included for the sludge cake (I) prepared by the process.