Spatial distribution of iron oxidation in the aerobic cells of the Wheal Jane Pilot Passive Treatment Plant.

The wetland cells of the Wheal Jane Pilot Passive Treatment Plant (PPTP) were designed to promote aerobic oxidation and precipitation of iron which could exceed a concentration of 100 mg l-1 in the raw mine water. The largest investment of land area was to the wetland (also called aerobic) cells and it was important to understand the processes of oxidation and precipitation of iron so that the performance of this part of the pilot passive treatment plant (PPTP) could be managed efficiently. The results of a high-resolution sampling programme on the distribution of Fe(II) within the first wetland cell of each treatment system are described. Comparison of inflow and outflow concentrations of iron adequately described the performance of the lime-dosed (LD) system. However, precipitation of iron in the anoxic limestone drain (ALD) and lime-free systems (LFS) was more efficient. On average, about 90% of the iron present in the inflow was removed using only 50% and 33% of the first aerobic cells of the ALD and LFS systems, respectively. As the concentration of iron approached 20 mg l-1, the rate of oxidation slowed considerably. This was probably due to be due to low pH levels caused by hydrolysis of Fe(III). With the introduction of passive pH control mechanisms, there was capacity to increase the volume of mine water treated by the ALD and LDS systems by 10 and 15 times, respectively, but it is uncertain as to whether or not other aspects of the passive treatment system would have sufficient capacity to deal with the increased volumes of mine water.

Clinical use of heparin-coated cardiopulmonary bypass in coronary artery bypass grafting.

Clinical handling, risk and benefit of a heparin-coated cardiopulmonary bypass system combined with reduced systemic heparinization in coronary bypass surgery was investigated in a prospective, randomized clinical study. 243 patients (Pts.) were divided into 3 groups: group A (n = 83) had a standard uncoated extracorporeal circulation (ECC) set, and systemic heparin was administered in an initial dose of 400 IE/kg body weight. During ECC activated clotting time (ACT) was kept > or = 480 sec. Group B (n = 77) had the same ECC set completely coated with low-molecular-weight heparin; i.v. heparin was given in the same dose as in group A, ACT was kept at the same level. Group C (n = 83) had the same coated ECC set as group B, but i.v. heparin was reduced to 150 IE/kg, and was set to be > or = 240 sec during ECC ACT. The same circulatory components were used in all 3 groups including roller pumps, coronary suction and an open cardiotomy reservoir. In the postoperative clinical course, recovery was not significantly different between groups, especially with respect to organ dysfunction; but there was significantly reduced postoperative bleeding where heparin-coated ECC and low-dose systemic heparinization were both used. This circulatory technique was also associated with a distinctly lower need for postoperative blood replacement. We conclude that heparin-coated extracorporeal circulation combined with either full-dose or reduced systemic heparinization can be used effectively with the same standard equipment and procedures as in uncoated technology. Combination with low-dose i.v. heparin leads to significantly decreased blood loss and less need for blood replacement.