The objective of this study was to deepen the understanding on the behavior of biopolymers in the integrated membrane system (IMS) for the reclamation of municipal wastewater effluent, with the final goal of obtaining insights for better fouling control of the reverse osmosis (RO) membrane. Experimental data showed that alginate-like polysaccharide (ALP) is a major kind of biopolymer and accounts for 48–64% in secondary wastewater effluent (SWE) . However, although it is well-known that alginate forms multimers larger than 0.1 μm in the presence of calcium ions (Ca²⁺) , experimental data showed that biopolymers in SWE were not removed by a virgin 0.1 μm microfiltration (MF) membrane. This result could be explained by the block fractions of ALP in SWE. Specifically, it was found that the majority (～70%) of ALP in SWE was categorized in the MM block, which has lower affinity to Ca²⁺ than GG or MG blocks, and that the percentage of GG block, which has the highest affinity to Ca²⁺ than other types of blocks, was only 5.1–6.3%. Nonetheless, up to 62% of biopolymer, mainly polysaccharide, was removed by a fouled MF membrane.

To accurately measure heavy metals contained in sediment, we investigated a method of reducing the amount of residue by decomposing sediments using a microwave-assisted method, which has become increasingly popular in recent years. It is known that the addition of hydrofluoric acid is essential for the digestion of samples containing silicon, but it also produces insoluble white precipitates containing Ca, Mg, and Al. In this study, scanning electron microscopy (SEM) observation revealed that the precipitates produced in the microwave-assisted digestion of silica-sand-rich tidal flat sediment contained heavy metal elements such as Fe and Mn. With this information heat treatment with perchloric acid was introduced to the protocol to dissolve the precipitates. By applying this analysis method to various environmental samples, the contents of Cr, Cu, and Zn in the sediment samples were found to increase by 40%, 20%, and 18%, respectively, on average compared with a conventional method. The method studied in this research provides more accurate quantification of heavy metal contents in sediment and will be useful for establishing analytical methods in the future.

We investigated the effect of phosphorus concentration control in basin sewerage on the decline of the juvenile clam population in the Toyogawa River mouth area in eastern Mikawa Bay from October 2018 to March 2019. In FY2018, the chlorophyll a concentration in the tidal flat was higher than that in FY2016 before the management of nutrient supply in the autumn and winter. The survival rates of juvenile clams born before autumn in 2018 were higher than those in FY2016. Juvenile clam (S.L. ≦ 300 μm) settled from October 2018 to January 2019 and grew up toward March while maintaining the population density. The picoplankton and nanoplankton of the 0.2–10 μm size fraction proliferated, as inferred from the amount of phosphorus released from the sewer when the daily variation of phosphorus load from Toyogawa River decreased from November 2018 to March 2019. The presence densities of settled juvenile clam (S.L. ≦ 300 μm) and early juvenile clam (300 < S.L. ≦ 500 μm) correlated with the chlorophyll a concentration of the size fraction of 0.2–10 μm. Phosphorus supplied during the concentration control operation maintained a suitable feeding environment for juvenile clam through the proliferation of phytoplankton.