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Oxygen demand, nitrogen and copper removal by free-water-surface and subsurface-flow constructed wetlands under tropical conditions

Lim PE, Wong TF, Lim DV

Environ Int, 2001 May;26(5-6):425-31.
PMID: 11392762

This study was conducted to: (1) assess the role of wetland vegetation in the removal of oxygen demand and nitrogen under tropical conditions, (2) estimate the uptake of nitrogen and copper by wetland plants and (3) investigate the speciation of Cu in wetland media among four operationally defined host fractions, namely exchangeable, carbonate, reducible and organically bound. Four laboratory-scale wetland units, two free-water-surface (FWS) and two subsurface-flow (SF) with one of each planted with cattails (Typha augustifolia), were fed with primary-treated sewage and operated at nominal retention times of 0.6-7 days. The influent and effluent BOD/COD and nitrogen concentrations were monitored to assess the performance of the wetland units for various mass loading rates. At the end of the study, all cattail plants were harvested and analyzed for total Kjeldahl nitrogen (TKN). Four other wetland units, which were identical to the first four, were fed with domestic wastewater spiked with copper in increasing concentrations. Copper speciation patterns in the sand layer were determined at the end of the study. The results showed that wetland vegetation did not play an important role in oxygen demand removal but were capable of removing about 22% and 26% of the nitrogen input in the FWS and SF wetland units, respectively. Mass balance analysis indicated that less than 1% of copper introduced was taken up by the cattails. Copper speciation patterns in the sand media showed that the exchangeable fraction contributed 30-57% and 63-80% of the nonresidual copper in the planted and unplanted FWS wetlands, respectively. For SF units, the percentages were 52-62% and 59-67%, respectively. This indicates that large amount of copper in the media were potentially remobilizable.
Fulltext Anaesthetic challenges in a morbidly obese man for cardiac myxoma resection: A case report

Chua CC, Wong TF, Ang CY, Yeap BT

Ann Med Surg (Lond), 2021 Nov;71:102998.
PMID: 34840753 DOI: 10.1016/j.amsu.2021.102998

Background: Cardiac myxoma is a rare neoplasm with female preponderance. It is the commonest benign cardiac neoplasm. We report a case entailing the perioperative anaesthetic challenges in managing a young morbidly obese man with a huge left atrial myxoma, who presented to us with acute symptoms of heart failure.
Case presentation: A young morbidly obese man with a body mass index (BMI) of 43.3 kg/m2 presented to us with acute symptoms of heart failure. An urgent transthoracic echocardiogram showed a huge pedunculated mass which arise from the left atrium, which occasionally completely occludes the mitral valve during each diastole. He underwent a resection of cardiac myxoma, which was complicated with intraoperative hypotension. Fortunately, it was successfully managed by placing the patient in Trendelenburg position for optimum blood pressure control.
Discussion: Tumours of the heart are very rare. Common histopathological findings are myxomas, followed by uncommon types of rhabdomyosarcomas and angiosarcomas. Pedunculated cardiac tumours can cause partial to complete obstructions which may lead to devastating conditions. Anaesthesia for morbidly obese patients with pedunculated cardiac myxoma are extremely challenging. Cardiac anaesthetists should be vigilant in managing these patients as they posed many life-threatening complications.
Conclusion: Cardiac myxoma are uncommon benign tumor of the heart with higher preponderances on the left atrium. Pedunculated mass can cause obstruction by limiting left ventricular filling, mimicking severe mitral stenosis. Positioning the patient Trendelenburg can transiently reduce intracardiac obstruction, improve cardiac output and venous return to the heart. Optimum patient positioning and management will lead to excellent outcomes.

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