Effect of using different proportions of inoculum during bioleaching on sludge dewaterability.

Bioleaching, the addition of bacteria to geological materials, has been applied to sludge to remove metals and improve upon sludge dewaterability. This paper investigates the effect of using different quantities of inoculum (bacteria) during bioleaching on sludge dewaterability. The analysis was based on bioleaching experiments conducted in a 20 L bio-reactor using different quantities of inoculum (20%, 10%, 5%, 2%, 0%). Changes in pH, oxidation reduction potential (ORP), capillary suction time (CST), specific resistance to filtration (SRF) and extracellular polymeric substances (EPS) were determined to gauge sludge dewatering. Results indicate that sludge dewaterability during the 2%, 10%, and 20% inoculum experiments declined through time. Decreased dewaterability is attributed to increases in the quantity of proteins and polysaccharides in slime EPS. Dewaterability improved during the 5% inoculum experiment, and reached a maximum when pH was 2.3. During this latter experiment, CST and SRF were reduced by 74% and 62%, respectively, in comparison to control conditions, while total EPS content decreased by 71%. The decrease in total EPS was primarily due to a decrease in proteins associated with tightly bound EPS (TB-EPS). Thus, changes in the amount of proteins in TB-EPS and sludge pH played a crucial role in sludge dewaterability.

Monitoring tidal flat dynamics affected by human activities along an eroded coast in the Yellow River Delta, China.

The coast of the northern Yellow River Delta (YRD) has experienced significant erosion since 1976 due to avulsion and consequent lack of sediment supply. Moreover, massive reclamation activity, expansion of the oil industry, and sea-level rise have jointly contributed to the rapid change of tidal flats over recent decades. Therefore, accurate reporting of the coast spatial extent and stability status is urgently required. We presented a method using remotely sensed waterlines to map tidal flats and monitor their spatiotemporal dynamics. The empirical results show that the area of the intertidal zone west of Tiao River Mouth (TRM) appeared to be decreasing. Despite intense hydrodynamic force, the intertidal zone to the east of TRM has expanded due to law prohibiting land reclamation in nature reserve. However, this trend weakened due to the expansion of oil industry after 2007. The movement of the mean high-tide line is the main cause for the increase-decrease patterns of the intertidal zone area. To achieve and maintain land equilibrium in this area, we suggest that a 554-m buffer must be preserved for mean high-tide line retreat. Unfortunately, the shrink crisis of the tidal flats has been extremely severe. Future reclamation and oil projects must be supplemented by studies that evaluate the complexities and dynamics of tidal flats so as to prevent the loss of this unique ecosystem.

Human impact on suspended particulate matter in the Yellow River Estuary, China: Evidence from remote sensing data fusion using an improved spatiotemporal fusion method.

Transport of suspended particulate matter (SPM) in estuarine waters plays an important role in regulating erosion-accretion and biogeochemical processes. In the Yellow River Estuary (YRE), artificial water and sediment regulation scheme (WSRS) and coastal engineering structures are the 2 typical anthropogenic activities affecting the spatiotemporal dynamics of estuarine SPM. The monitoring of SPM transport affected by such human activities requires SPM mapping at both high spatial and high temporal resolutions. In this study, we presented an improved Flexible Spatiotemporal Data Fusion (FSDAF) strategy with consideration of highly dynamic SPM variations in estuarine waters, and generated 30-m hourly SPM concentrations based on Landsat 8 OLI and GOCI datasets. The new strategy produced higher SPM estimation accuracy than the original FSDAF, with the relative percentage difference (RPD) decreasing from 29.75% to 5.31% using GOCI-derived hourly SPM as reference. With in situ SPM measurements as reference, the fused SPM concentrations had an RMSE of 12.09 mg/L and an RPD of 27.17%. Investigation of interday SPM variations before, during, and after the WSRS in 2018 revealed that the first WSRS significantly increased the SPM concentration and plume extent; new wetland with an area of 12.56 km2 was formed due to sediment accretion near the river mouth. The two groins offshore from the coastlines on the north and south sides of YRE exhibited obvious sediment trapping effects in that higher SPM concentrations on one side of each groin were found regardless of the turbidity modes and diurnal SPM variations; the trapping effects were associated with the number of groins and groin length. Intraday variations of SPM were influenced by tidal currents, with plume direction following the ebb and flooding tidal current direction. The inter- and intraday characteristics of the 30-m hourly SPM dynamics facilitate the detailed analysis of the sediment transport associated with human activities.