Engineering and microstructure properties of contaminated marine sediments solidified by high content of incinerated sewage sludge ash

Management of incinerated sewage sludge ash(ISSA)and dredged contaminated marine sediments(CMSs)is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity.The present study investigates the use of high content(20%of sediment by mass)of ISSA in combination with cement/lime for solidification/stabilization(S/S)treatment of CMSs to provide a way to reuse the wastes as construction materials.The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content(w80%).The S/S treatment improved the engineering properties of the sediment,but reduced the workability,especially for the lime-treated samples.Lime can be used to replace ordinary Portland cement(OPC)for better heavy metal immobilization and carbon emission reduction.The hardened sediment samples prepared with 10%of lime and 20%of ISSA could attain a strength of 1.6 MPa after 28 d of curing.In addition,leaching tests confirmed that there was no environmental risk induced by these stabilized materials.The formation of hydrated cementitious compounds including calcium silicate hydrate(CeSeH)/calcium aluminate silicate hydrate(C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.

Carbon-negative cement-bonded biochar particleboards

Biochar from bio-waste pyrolysis presents excellent CO_(2) sequestration capacity.This study innovated the design of cement-bonded particleboards utilizing a substantial amount of 50-70 wt.%pre-soaked biochar to render the products carbon-negative.We investigated the roles of biochar in magnesium oxysulfate cement(MOSC)system and demonstrated good mechanical and functional properties of biochar cement particleboards.In the presence of biochar,the amounts of hydration products were enriched in the cement systems as illustrated by the thermogravi-metric analyses(TGA)and X-ray diffraction(XRD).We further incorporated supplementary cementitious materials(SCMs)and generated 5 Mg(OH)_(2)⋅MgSO_(4)·7H_(2)O(5-1-7)phase in the MOSC system.As a result,our designs of biochar particleboards satisfied the standard requirements for flexural strength(>5.5 MPa)and thickness swelling(<2%).Moreover,our biochar particleboards presented a low thermal conductivity as the biochar pores disrupted thermal bridging within particleboards.We illustrated that the high dosage ratio of biochar could significantly offset the CO_(2) emissions of the particleboards(i.e.,carbon-negative)via life cycle assessment.Noticeable economic profits could also be accomplished for the biochar particleboards.For instance,the 50BC-MOSC bonded particleboard(with 50 wt.%pre-soaked biochar as aggregate,50 wt.%MOSC as binder)with promising mechanical properties could store 137 kg CO_(2) tonne^(−1) and yield an overall economic profit of 92 to 116 USD m^(−3) depending on the carbon prices in different countries.In summary,our new designs of carbon-negative biochar particleboards could curtail carbon emissions in the construction materials and promote the realization of carbon neutrality and circular economy.

Agronomic effectiveness of recovered phosphate fertilizer produced from incinerated sewage sludge ash

Phosphorus(P)recovery from incinerated sewage sludge ash(ISSA)has been extensively investigated,but insufficient research has been conducted to evaluate the effect of different kinds of recovered phosphate fertilizers(RPFs)on plant growth with respect to the P and heavy metal contents of RPFs.In this study,three kinds of RPFs,precipitated calcium phosphate fertilizer(CaP),struvite phosphate fertilizer(SP),and P-loaded biochar(BP),produced from ISSA were characterized,and their agronomic effectiveness was verified by hydroponic and soil cultivation.In addition to the three kinds of RPFs,a control group(mono-phosphate fertilizer in hydroponic group/compound fertilizer in soil cultivation group)and a blank control group(BC,with zero P)were tested on choy sum and ryegrass at the same time.SP has the highest P purity(76.0%of struvite)while the BP has the most complex P species(P was co-exist with Fe,Al,and Mg).Plant growth results showed that the RPFs greatly facilitated plant growth and demonstrated superior/comparable effects to those of control group.In hydroponics testing,SP showed the best effect(shoot length of 17.0 cm,chlorophyll content of 2.05 mg/g)due to the Mg involved and the high P purity of SP,while BP performed the best(shoot length of 13.7 cm,chlorophyll content of 2.42 mg/g)in the soil testing system among all of the groups because of the additional nutritional elements and the high P availability of BP.Additionally,the accumulation of heavy metals in the plants under all conditions did not exceed the limits stipulated in the regulations.These results indicate that recovering P from ISSA is an attractive technology to produce P fertilizers,which can alleviate both the scarcity of phosphate resources and the burden of ISSA management.

Correction to:Agronomic effectiveness of recovered phosphate fertilizer produced from incinerated sewage sludge ash

In this article,the affiliation details for Author Chi Sun Poon were incorrectly given as'State Key Laboratory of Water Environment Simulation,School of Environment,Beijing Normal University,Beijing 100875,China'and'State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China'but should have been'Department of Civil and Environmental Engineering,The Hong Kong Polytechnic University,Kowloon,Hong Kong,China'and'IRSM-CAS/HK PolyU Joint Laboratory on Solid Waste Science,Kowloon,Hong Kong,China'.The original article has been corrected.