Characterization of Scale Formed on the Surfaces of Toilet Bowls

Abstract

Repeated use of a toilet results in the build-up of a deposit derived from urine and hard water on the surface of the toilet bowl. The hardened mineral scale is difficult to clean completely, especially in the case of deposits under the rim. A number of studies have focused on kidney stones, which are also caused by urine in the urinary tract; little attention, however, has been paid to the detailed composition and structure of the toilet scale. To develop powerful products for removing the toilet scale effectively instead of relying on acid-cleaning and scrubbing, the composition and the accumulation mechanism of the scale must be clarified. Scale samples collected from the bowl surface were characterized by IR, XRF, XRD, ICP-AES, SEM-EDS and HPLC techniques and found to consist mainly of calcium phosphates, struvite, calcium carbonate, uric acid and proteins. After acid treatment of the scale, a film-like structure of protein, produced as a result of the metabolism of bacteria and mold, was left behind. The scale had composite structures that were composed of the inorganic minerals and the organic materials listed above. This structure might be critical to making the scale resistant to removal by acid-containing cleaners.

Characterization of urea hydrolysis in fresh human urine and inhibition by chemical addition

“…1,2 Urea hydrolysis via the urease enzyme is also the cause of operating problems with urine-diverting toilets and nonwater urinals. [3][4][5][6][7] The reaction involves urea, an abundant compound found in the environment and human urine, 8 hydrolyzing to form ammonia and bicarbonate resulting in an elevated pH of the surrounding soil or solution. 9 Hydrolysis requires the urease enzyme, which is a metalloenyzme with two nickel ions per catalytic unit in the active site.…”

“…14 Urine diversion processes are susceptible to the urea hydrolysis reaction due to urine's high urea content, and the ubiquitous presence of bacteria and bacterial urease on bathroom fixtures and on the human body. 3,5,17 Urea hydrolysis in urine diversion systems is especially detrimental due to the formation of calcium and magnesium phosphates that form after hydrolysis has occurred in the urinals, pipes, and storage tanks of undiluted urine. 4,5,9 The precipitates that form are hard minerals that are not easily removed.…”

“…3,5,17 Urea hydrolysis in urine diversion systems is especially detrimental due to the formation of calcium and magnesium phosphates that form after hydrolysis has occurred in the urinals, pipes, and storage tanks of undiluted urine. 4,5,9 The precipitates that form are hard minerals that are not easily removed. 18,19 This results in frequent and expensive cleaning and maintenance.…”

Mimicking and Inhibiting Urea Hydrolysis in Nonwater Urinals

“…The urease enzyme is produced by a wide range of organisms, from eukaryotes to prokaryotes, and is most active as the bacterial urease in wastewater collection systems. , The addition of ammonia, bicarbonate, and hydroxide via urea hydrolysis raises the pH of fresh urine from pH 6 to pH 9 and creates supersaturated conditions for precipitation of phosphate minerals, such as struvite (NH 4 MgPO 4 ·6H 2 O) and hydroxyapatite (Ca 5 (PO 4 ) 3 (OH)). ,, A study on scale formation on conventional flush toilets bowls found that 65% of the scale was due to the precipitation of struvite, calcium phosphate, and calcium carbonate, with the remaining 45% of scale being organic-based solids . Research on urine diversion systems has indirectly investigated urea hydrolysis by studying the rate, extent, and type of minerals that precipitate in urine. ,, Previous research that has directly investigated the urea hydrolysis reaction and its inhibition is mostly from soil science and microbiology. − According to Ray et al, urea hydrolysis inhibitors most commonly found in soil science literature were not able to inhibit urea hydrolysis in urine due to the presence of competing ions .…”

“…18,20,21 A study on scale formation on conventional flush toilets bowls found that 65% of the scale was due to the precipitation of struvite, calcium phosphate, and calcium carbonate, with the remaining 45% of scale being organic-based solids. 22 Research on urine diversion systems has indirectly investigated urea hydrolysis by studying the rate, extent, and type of minerals that precipitate in urine. 18,23,24 Previous research that has directly investigated the urea hydrolysis reaction and its inhibition is mostly from soil science and microbiology.…”