Extracting phosphorus and other elements from lake water: Chemical processes in a hypolimnetic withdrawal and treatment system

Hypolimnetic withdrawal provides a way to remove phosphorus (P) from eutrophic lakes, but the method is still rarely combined with water treatment for capturing this P. Thus, little is known about the chemical interactions of P and other elements upon the treatment of hypolimnetic lake water. We investigated these chemical processes in a hypolimnetic withdrawal and treatment system (HWTS) in which hypolimnetic water is first led into a treatment unit for dissolved P (dP) precipitation and subsequently filtered before being circulated back into the lake. We studied three different field-scale treatment unit setups and water treatments (aeration only, aeration + calcium hydroxide (Ca(OH)₂), aeration + biopolymer) to compare their effectiveness for dP removal and the geochemical properties of the resulting precipitate. In the aeration only treatment, most of the dissolved iron (dFe) (91-95%) and dP (71-91%) were removed when sand filters were used. The addition of Ca(OH)₂ and biopolymer enhanced Fe flocculation, leading to more effective removal of dFe (d99-100%) and dP (88-95%) from the water. Regardless of the water treatment method, dP was always precipitated by amorphous Fe oxides formed in the hypolimnetic water upon aeration. The P content of the resulting precipitates was somewhat lower than expected (2 439-4 145 mg kg^-1), which may be linked to chemical interactions between Fe and other components in the hypolimnetic water, such as organic matter. The precipitates also contained some heavy metals such as copper and zinc. We conclude that all the tested water treatments were effective in removing dP from hypolimnetic water, but the enhanced precipitation by the addition of treatment chemicals is beneficial when a mesh or other rapid filtration method is used, or when there is only negligible accumulation of dFe in the hypolimnion of the treated lake. Depending on the water treatment method and the water chemistry of the treated lake, the precipitate may have potential for nutrient recycling, although it may sometimes require preliminary processing to enhance bioavailability for plants and to reduce the concentration of heavy metals.

The carry-over effect on the bowel habit in elderly long-term patients of long-term bulk-forming products containing stimulant laxative

This study was undertaken to investigate the possible carry-over effect on elderly long-term patients of bulk-forming products containing stimulant type laxatives. Thirty-six patients received magnesium hydroxide daily for a mean period of 10 months prior to the study, and 23 patients received bulk laxatives containing cassiae senna daily for a mean period of 13 months prior to the study. The pre-study laxatives were randomly changed either to magnesium hydroxide or to bulk laxatives. In the patient group receiving a bulk-forming product containing stimulant type laxative long-term prior to the study, the need for additional stimulant laxatives during the pure bulk laxative (3.0 vs. 3.8/4 weeks, NS) or magnesium hydroxide treatment (2.6 vs. 2.7/4 weeks, NS) was not more frequent and the frequency of defaecation was not lower than in the patients (during bulk laxative 11.2 vs. 9.3/4 weeks, NS and during magnesium hydroxide 12.0 vs. 13.7/4 weeks, NS) who received long-term magnesium hydroxide treatment prior to the study. Thus, our data indicated no carry-over effect after the use of bulk-forming laxatives containing senna for 13 months in elderly long-term patients.

Safety and efficacy of a bulk laxative containing senna versus lactulose in the treatment of chronic constipation in geriatric patients

Thirty geriatric long-stay patients aged 65-94 years (mean 81.8) participated in the trial the aim of which was to examine bulk laxative plus senna (Agiolax) in the treatment of chronic constipation using lactulose (Levolac) as a reference medicine. Bulk laxative plus senna (daily doses 14.8 g) produced more frequent (p < 0.05) bowel habits (4.5 vs. 2.2-1.9/week) than lactulose (daily doses 20.1 g). Both laxatives proved to be safe to use. Our study indicated bulk laxative plus senna to be more efficient in treating constipation in geriatric long-stay patients.

Study of constipation in a geriatric hospital, day hospital, old people's home and at home

A study of constipation and related factors was carried out in 439 geriatric hospital patients, 183 people living in two old people's homes, and 78 patients visiting a geriatric day hospital. In addition, a cross-sectional survey of constipation and related factors was undertaken in 138 people older than 74 years and 74 people aged 41 to 50 years living at home. Constipation and the use of laxatives were most frequent in the geriatric hospital (79% and 76% respectively), followed by the old people's homes (59% and 60%), the day hospital (29% and 31%), elderly living at home (38% and 20%) and middle-aged living at home (12% and 5%). The results suggest an increased risk of constipation for the persons walking less than 0.5 km daily [relative risk (RR) = 1.7], walking with help (RR = 3.4), chairbound (RR = 6.9) and bedbound (RR = 15.9). The relative risk of constipation increased for the persons living in the old people's homes (RR = 1.7) and the geriatric hospital (RR = 2.2), and also with advancing age (between 75 and 84 years, RR = 2.9; over 84 years, RR = 4.9). The prevalence of constipation was directly correlated to fecal and urinary incontinence.

Diarrhea and fecal impaction in elderly long-stay patients

A retrospective screening of one year's duration was carried out on 245 permanently hospitalized geriatric patients to study the frequency and cases of periods of at least three days' diarrhea. Such periods were suffered by 65/245 patients and 32% had recurrencies. Fecal impaction was the most common cause of diarrhea (in 55%). Diarrhea was induced by laxatives in 20%. Gastrointestinal infections caused 5% of the diarrhea cases. Immobility and fecal incontinence were strongly associated with fecal impaction in cases of diarrhea. Urinary tract infections treated with antibiotics in the patients with fecal impaction and diarrhea almost were twice as frequent as in patients with other causes of diarrhea or patients with no diarrhea. This retrospective investigation emphasizes the importance of the recognition and proper treatment of constipation, especially in bedridden or chairbound elderly persons with fecal incontinence and diarrhea.

Comparison of the effects of magnesium hydroxide and a bulk laxative on lipids, carbohydrates, vitamins A and E, and minerals in geriatric hospital patients in the treatment of constipation

In a crossover study the effects of magnesium hydroxide on serum lipids, carbohydrates, vitamins A and E, uric acid and whole blood minerals were compared with those of a bulk laxative containing plantago rind and sorbitol in 64 constipated, elderly long-stay patients, 55 of whom were receiving diuretics. Hypomagnesaemia occurred in 11 (17%) patients after bulk laxative and in two (2%) patients after magnesium hydroxide treatment. There was a slight reduction in low values of high-density lipoprotein cholesterol and high values of triglycerides after magnesium hydroxide treatment. There were no significant differences in plasma lipids, whole blood minerals or vitamins A and E using either laxative. Negative correlations were found between the increase in serum concentrations of magnesium and glycosylated haemoglobin A1 (P less than 0.02) and the serum level of uric acid (P less than 0.01). These results suggest that the long-term effects of magnesium hydroxide and bulk laxative on the absorption of nutrients may not be significantly different. Magnesium hydroxide, however, may have beneficial effects on lipid disorders, impaired glucose tolerance and hyperuricaemia in magnesium deficiency due to diuretics and thus may be a favourable laxative for use in bedridden geriatric patients receiving diuretics.