N, P, and COD conveyed by urban runoff: a comparative research between a city and a town in the Taihu Basin

Stormwater runoff containing various pollutants exerts adverse effects on receiving water bodies and deteriorates the urban aquatic environment. Although numerous studies have been conducted on runoff pollution, research comparing its characteristics in cities with those in towns is rare in the literature. To close this gap, the present study was conducted. The outflow concentration and peak value of N in the town were higher than those in the city in most conditions (at 75% and 67%, respectively). The second peak value of P in the town was higher and occurred earlier than the city. EMCs of TN and DTN in the town were 20%–60% (10%–50%) higher than those in the city. DTP accounted for 76.9%–83.3% of the total P (TP) in the town, which was generally higher than the city values of 50%–87.5%. According to our results, road runoff in the town contributed more to urban aquatic pollution, thus further research should concentrate on this particular type of runoff.

Vertical-flow constructed wetlands treating domestic wastewater contaminated by hydrocarbons

The aim was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand (COD) loading) variables on the long-term and seasonal performance of vertical-flow constructed wetland filters operated in tidal flow mode before and after a one-off spill of diesel. Ten different vertical-flow wetland systems were planted with Phragmites australis (Cav.) Trin. ex Steud. (common reed). Approximately 130 g of diesel fuel was poured into four wetland filters. Before the spill, compliance with secondary wastewater treatment standards was achieved by all wetlands regarding ammonia-nitrogen (NH4-N), nitrate-nitrogen (NO3-N) and suspended solids (SS), and non-compliance was recorded for biochemical oxygen demand and ortho-phosphate-phosphorus (PO4-P). Higher COD inflow concentrations had a significantly positive impact on the treatment performance for COD, PO4-P and SS. The wetland with the largest aggregate size had the lowest mean NO3-N outflow concentration. However, the results were similar regardless of aggregate size and resting time for most variables. Clear seasonal outflow concentration trends were recorded for COD, NH4-N and NO3-N. No filter clogging was observed. The removal efficiencies dropped for those filters impacted by the diesel spill. The wetlands system shows a good performance regarding total petroleum hydrocarbon (TPH) removal.

Quantitative assessment of luminal stirring in the perfused small intestine of the rat

We measured the resistance (RL) to CO absorption that resulted from poor luminal stirring in the constantly perfused rat jejunum. RL or calculated unstirred layer thickness was greater for 30-cm than 10-cm long segments, indicating lack of a uniform thickness of unstirred layer. The possibility that laminar flow existed in the gut was first tested by calculating expected CO absorptions from fluid moving with laminar flow. These values agreed closely with observed absorption rates. Laminar flow also was supported by the observation that CO absorption was independent of perfusate viscosity. Lastly, after sudden addition of phenolsulfonphthalein (PSP) to the perfusate, PSP outflow concentration was similar in tygon tubing (which has laminar flow) and a gut segment of comparable dimension. We conclude that flow in the perfused gut is laminar and that this laminar flow has many implications for studies carried out with the constant-perfusion technique.

Regional tissue uptake of D2O in perfused organs: rat liver, dog heart and gastrocnemius

Regional tissue D2O concentrations were measured in the isolated dog heart, dog gastrocnemius and rat liver following relatively brief perfusions with D2O-labeled fluid. Results indicate heterogeneity of tissue concentrations in all three organs. A venous outflow concentration curve for the liver was reconstructed on the assumptions that each regional tissue sample represented an equally probable portion of a composite organ and that in each region D2O transport was flow-limited. The agreement between this curve and the observed outflow curve was sufficiently good to suggest that the discrepancies between the observed venous curve and that for the theoretical case of a completely flow-limited organ can be largely explained for the liver by macroscopic regional perfusion heterogeneity without invoking microscopic tissue transport limitation. In the case of the heart and the gastrocnemius, the observed macroscopic tissue heterogeneity was insufficient to account for the discrepancies between the respective venous outflow concentration curves and the theoretical case. However, in the heart, regions of low tissue concentration were apparently systematically missed in the sampling procedure. The actual heterogeneity in both organs was probably underestimated.