VALORIZATION OF PAPER INDUSTRY LIME SLUDGE, BOILER ASH AND ETP SLUDGE

Abstract

The industrial solid waste generation and its stockpile disposal have major environmental consequences. These consequences could be minimized through the solid waste application as a raw material in other industries. The current thesis focusses on application of paper industry solid waste in different applications like nanosilica synthesis, cementitious binder fabrication, application in concrete and methanogenesis. Graphical Abstract Boiler ash is utilized for the synthesis of nanosilica. The particle size of synthesized particles were found in the range of 10-25 nm. . FTIR, TEM and XRD studies confirmed the synthesis of nanosilica. Present study shows about 250 kg of nanosilica can be synthesized per ton of boiler ash with the nanosilica synthesis efficiency of almost 25%. Lime sludge application with nanosilica reduces the temperature of belite synthesis to 1000°C without addition of any chemical stabilizer and pre-calcination whereas conventionally, belite is synthesized above 1200°C. This method of belite based clinker synthesis is energy efficient and ecofriendly. The prepared clinker was mixed with Ground granulated blast furnace slag (GGBS) for the increment in early age strength as belite generally takes part in the development of late strength of concrete. The heat of hydration of developed binder, compressive strength and density of the prepared mortars complies the requirements of indoor and outdoor mortar applications. Lime sludge is also being utilized directly in the concrete with synthesized nanosilica and without ii nanosilica. The purpose was to increase the proportion of lime sludge application in concrete without affecting the compressive strength significantly. It provides a novel and relevant approach for bulk utilization of lime sludge with application of nanosilica synthesized from fly ash. This research will also be relevant for onsite utilization of paper industry boiler ash and lime sludge. It will cut down the transportation expenses of lime sludge and boiler ash disposal or utilization. Application of lime sludge with nanosilica in M25 grade of concrete found suitable. The concrete blocks with 30% application of lime sludge and 1% nanosilica produced sustainable concrete with increased compressive strength. 1% nanosilica addition with lime sludge resulted in 25% increased compressive strength in comparison to the blocks without nanosilica. It provides an edge of the 3 times more application of lime sludge and 30% less consumption of cement in concrete blocks without affecting the compressive strength significantly. The FE-SEM micrographs of concrete with 30% lime sludge and different proportion of nanosilica show a trend of increasing uniformity and microstructure compaction with increasing amount of nanosilica. Study provides a suitable route of value addition and valorization for lime sludge and fly ash. As another route of bulk utilization of lime sludge, it is also utilized with calcination at lower temperature than normal calcination temperature. The lime sludge is calcined at lower temperature of 650° C to convert metakaolinite in kaolinite. The MK (metakaolinite-Al₂O₃.2SiO₂) can make the lime sludge more reactive which makes it perfect raw material to use as cement additive. Al2Si2O5 (OH) 4 = Al2Si2O7 + 2H2O (1) (Kaolinite) (Metakaolinite) Lime sludge calcined at low temperature of 650 °C can be applied productively as a pozzolana with cement. Compressive strength of produced concrete remains intact until 30% application of calcined lime sludge in binder. The pozzolanic behavior of lime sludge is due to the metakaolinite and calcium oxide produced after calcination of lime sludge at 650 0C. These are the sole reasons for increased lime sludge reactivity and accumulation of increased amount of calcium silicate hydrate (CSH) and hydrates of tetra calcium aluminates (TAH). The. Morphological study of concrete and heat of hydration of prepared binder also confirms the increased reactivity of lime sludge. The prepared binder is sustainable with 18% less production cost and emission of greenhouse gases. ETP sludge with cow manure is utilized for biogas production from anaerobic co-digestion (AD). It can stabilize the sludge with energy production at the same time. The AD process was performed at uncontrolled temperature in (450-700 0C) iii mesophilic range, which can be effective for small and medium scale of industries. The aim was to utilize the Paper ETP sludge (PSS) for the AD process and to Co-utilization of PSS with cow manure to check the effect of digestion. The reactor containing PPS only was started to generate biogas on 5th day of the reaction with 7.8% of methane. The cumulative methane yield attained to 13.5 ml/g volatile solid (VS) until day 30. The second reactor containing PPS and cow manure produced methane 134 ml/g VS until day 30. This study presents a more optimized process of anaerobic digestion of paper sludge and co-digestion of paper sludge with cow manure. The utilization of lime sludge and boiler ash of paper industry is recommended as material for construction applications while anaerobic digestion can be used for energy recovery from ETP sludge. These applications will also beneficial for reducing environmental wallop.