The　increasing　levels　of　sewage　sludge　production　demands　research　and　development　to　introduce　more　commercially　feasible　options　for　reducing　socio-economic　and　environmental　problems　associated　with　its　current　treatment.　Sewage　sludge　may　be　processed　to　produce　useful　products　or　as　a　feedstock　for　energy　generation.　Initially,　the　characteristics　of　sewage　sludge　are　discussed　in　terms　of　composition　and　the　current　options　for　its　treatment　with　the　associated　environmental　impacts.　Processes　to　valorize　sewage　sludge　are　discussed,　including　heavy　metal　removal　from　sewage　sludge,　production　of　bio-char,　production　and　use　of　activated　carbon　and　use　of　sewage　sludge　combustion　ash　in　cement　and　concrete.　Thermochemical　processes　i.e.,　pyrolysis,　co-pyrolysis　and　catalytic　pyrolysis,　also　gasification　and　combustion　for　process　intensification,　energy　and　resource　recovery　from　sewage　sludge　are　then　critically　reviewed　in　detail.　The　pyrolysis　of　sewage　sludge　to　produce　a　bio-oil　is　covered　in　relation　to　product　bio-oil　composition,　reactor　type　and　the　use　of　catalysts.　Gasification　of　sewage　sludge　focusses　on　the　characteristics　of　the　different　available　reactor　types　and　the　influence　of　a　range　of　process　parameters　and　catalysts　on　gas　yield　and　composition.　The　selection　and　design　of　catalysts　are　of　vital　importance　to　enhance　the　selectivity　of　the　selected　thermochemical　pyrolysis　or　gasification　process.　The　catalysts　used　for　sewage　sludge　treatment　need　more　research　to　enable　selectivity　towards　the　targeted　desired　end-products　along　with　optimization　of　parametric　conditions　and　development　of　innovative　reactor　technologies.　The　combustion　of　sewage　sludge　is　reviewed　in　terms　of　reactor　technologies,　flue　gas　cleaning　systems　and　pollutant　emissions.　In　addition,　reactor　technologies　in　terms　of　technological　strength　and　market　competitiveness　with　the　particular　application　to　sewage　sludge　are　compared　for　the　first　time　for　thermochemical　conversion.　A　critical　comparison　is　made　of　the　drying　techniques,　co-feedstocks　and　catalytic　processes,　reaction　kinetics,　reactor　technologies,　operating　conditions　to　be　optimized,　removal　of　impurities,　fuel　properties,　their　constraints　and　required　improvements.　The　emphasis　of　this　review　is　to　promote　environmental　sustainability　for　process　intensification,　energy　and　resource　recovery　from　pyrolysis,　gasification　and　combustion　involving　the　use　of　catalysts.　©　2020　Elsevier　Ltd