Effects of alkalinity on interaction between EPS and hydroxy-aluminum with different speciation in wastewater sludge conditioning with aluminum based inorganic polymer flocculant

Extracellular polymeric substances(EPS)form a stable gel-like structure to combine with water molecules through steric hindrance,making the mechanical dewatering of wastewater sludge considerably difficult.Coagulation/flocculation has been widely applied in improving the sludge dewatering performance,while sludge properties(organic fraction and solution chemistry conditions)are highly changeable and have important effects on sludge flocculation process.In this work,the alkalinity effects on sludge conditioning with hydroxy-aluminum were comprehensively investigated,and the interaction mechanisms between EPS and hydroxy-aluminum with different speciation were unraveled.The results showed that the effectiveness of hydroxy-aluminum conditioning gradually deteriorated with increase in alkalinity.Meanwhile,the polymeric hydroxy-aluminum(Al 13)and highly polymerized hydroxy-aluminum(Al 30)were hydrolysed and converted into amorphous aluminum hydroxide(Al(OH)3),which changed the flocculation mechanism from charge neutralization and complexing adsorption to hydrogen bond interaction.Additionally,both Al 13 and Al 30 showed higher binding capacity for proteins and polysaccharides in EPS than monomeric aluminum and Al(OH)3.Al 13 and Al 30 coagulation changed the secondary structure of proteins in EPS,which caused a gelation reaction to increase molecular hydrophobicity of proteins and consequently sludge dewaterability.This study provided a guidance for optimizing the hydroxy-aluminum flocculation conditioning of sludge with high solution alkalinity.

Mobile Sensing in the COVID-19 Era:A Review

Background. During the COVID-19 pandemic, mobile sensing and data analytics techniques have demonstrated their capabilitiesin monitoring the trajectories of the pandemic, by collecting behavioral, physiological, and mobility data on individual,neighborhood, city, and national scales. Notably, mobile sensing has become a promising way to detect individuals’ infectiousstatus, track the change in long-term health, trace the epidemics in communities, and monitor the evolution of viruses andsubspecies. Methods. We followed the PRISMA practice and reviewed 60 eligible papers on mobile sensing for monitoringCOVID-19. We proposed a taxonomy system to summarize literature by the time duration and population scale under mobilesensing studies. Results. We found that existing literature can be naturally grouped in four clusters, including remote detection,long-term tracking, contact tracing, and epidemiological study. We summarized each group and analyzed representative workswith regard to the system design, health outcomes, and limitations on techniques and societal factors. We further discussed theimplications and future directions of mobile sensing in communicable diseases from the perspectives of technology andapplications. Conclusion. Mobile sensing techniques are effective, efficient, and flexible to surveil COVID-19 in scales of timeand populations. In the post-COVID era, technical and societal issues in mobile sensing are expected to be addressed toimprove healthcare and social outcomes.