| With the development of economic,acceleration of urbanization,the efficiency of municipal sewage treatment has been improved year by year,large number of by-products-municipal sludge,are produced due to the treatment of municipal sewage.Considering the severe situation that the present treatment and disposal methods do not keep up with urban development,how to properly treat and dispose of sludge will become a core issue in the field of urban environmental pollution control.At the same time,reclaiming abundant phosphorus in sewage sludge to be used as a novel fertilizer via pyrolysis has gained increasing attention due to the rapid depletion of global phosphorus reserves.This study aimed at the efficient application of phosphorus in urban sludge pyrochar,and applied pyrolysis modification as the main method to comprehensively study the characteristics of sludge pyrolysis and the characteristics of volatile products release.By systematically studying the effects of different calcium-based additives on the migration of phosphorus during sludge pyrolysis,the effects of sludge pyrochar on soil physicochemical and microbial community were revealed when sludge pyrochar land utilization,and a novel sludge pyrochar modification strategy is proposed.The research results of this paper provide a theoretical and technical basis for realizing the reduction,stabilization,clean and efficient utilization of urban sewage sludge.In this paper,the TG-FTIR-MS three-machine combined real-time monitoring system was used as the main means to study the co-pyrolysis of sludge and coffee grounds and the pyrolysis characteristic of sludge.The study found that the volatile products released during sludge pyrolysis was concentrated at 330～500°C,and it showed a trend of increasing at first and then weakening with the increase of pyrolysis temperature.When the blending ratio（coffee grounds:sludge）is 3:7,it had a certain inhibitory effect on the release of volatile products.The addition of coffee grounds did not change the composition of sludge pyrolysis products,but increased the maximum weight loss efficiency of sludge;it was beneficial to the hot start process of sludge pyrolysis reaction and increased the effective collision frequency required for sludge pyrolysis reaction.In addition,through the determination of total phosphorus and the analysis of phosphorus species,it was found that phosphorus in low-temperature pyrolysis sludge pyrochar was mainly organic phosphorus,while phosphorus derived from high-temperature pyrolysis pyrochar was mainly inorganic phosphorus,such as Al-P and pyrophosphate.Studies showed that the blending of coffee grounds could increase the total phosphorus content,and when the blending ratio was 3:7,when pyrolysis is carried out at 500°C,the proportion of water-soluble phosphorus in the biochar is up to 44%.Therefore,the biochar generated by co-pyrolysis of sludge and coffee grounds has the potential to be used as a quick-acting fertilizer.During sludge pyrolysis,three common calcium-based additives—calcium oxide,calcium hydroxide,and calcium phosphate—promote the conversion of phosphorus in the sludge into a form of calcium and phosphorus available to plants（hydroxylapatite）,and an efficient strategy for phosphorus recovery from sludge was proposed.The solid-state NMR results showed that 76.8%of the pristine sludge pyrochar was Al2（OH）3PO4,and this form of phosphorus could not be used by plants;while the characterization results of phosphorus in the modified sludge pyrochar showed that the content of hydroxylapatite produced reached the peak by adding 10%Ca O,5%Ca（OH）2 or 10%Ca3（PO4）2.The thermodynamic simulation results show that the introduction of additives can increase the enthalpy of the pyrolysis system,and when the additive was Ca O,the system enthalpy was the lowest,which showed that the addition of Ca O during the sludge pyrolysis was more conducive to the recycling of phosphorus in the sludge as the form of hydroxylapatite.Moreover,when the pyrolysis temperature exceeds 900°C,the generated calcium hydroxylapatite was unstable and decreases sharply.Therefore,this study demonstrates the regulation of calcium-based additives（Ca/P ratio）as an effective strategy to recover phosphorus in the form of hydroxylapatite from sewage sludge,which verified the feasibility of recycling phosphorus from urban sludge to achieve global phosphorus resource sustainability.Through systematic analysis of soil physicochemical properties and soil microbiology during land-use of pyrochar,an effective improvement technology and cleaning application of calcium-based modified sludge pyrochar are proposed.The study found that adjusting calcium-based additives to promote the pyrolysis of sludge phosphorus positively affected ryegrass growth and soil microbial diversity.In the pot experiment,the modified sludge pyrochar mainly affected the growth of ryegrass by changing the content of available phosphorus and organic matter in the soil.In the groups treated with pyrochar prepared by Ca O and Ca（OH）2 addition,Ramlibacter was dominant,which can promote the conversion of phosphorus to hydroxylapatite;while in the groups treated with pristine sludge pyrochar addition,metal uptake-accelerating Massilia showed a high abundance in the group treated with pristine sludge pyrochar.In addition,the accumulation of Pb in the shoots of ryegrass plants in the calcium-based additive treatment group was less than 3%,but more than 35%of Pb was accumulated in shoots treated with pristine sludge pyrochar.Based on the analysis of macroscopic and microscopic information,it was concluded that phosphorus-enhanced sludge biochar can promote the growth of ryegrass,improve soil physicochemical properties,especially available phosphorus and organic matter,and prevent the metal transfer to ryegrass.Therefore,a smart,simple,and green application method of sludge pyrochar utilization was designed through in-depth research on the characteristics of sludge pyrolysis,the mechanism of phosphorus transfer and transformation in sludge,and the effect of sludge pyrochar on soil physicochemical properties and microorganisms. |
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