Waterless urinals save precious fresh water normally used for flushing and reduce odour levels in restrooms. However, existing models of waterless urinals available on the market are expensive and maintenance costs of the odour traps of these urinals are also quite high. Experiments conducted using a low cost membrane-based waterless-urinal odour prevention trap available in India revealed a reduction of over 90.5% in ammonia gas concentration in the urinals. The ammonia levels observed, in the range of 0.22 to 0.30 ppm in waterless urinals fitted with the odour trap evaluated in this study, is comparable to values reported for the widely used sealant liquid based waterless urinals in the past. No sign of clogging was observed in the clogging tests conducted. Passage of particles up to 4 mm in size in the particle flow analysis tests conducted is somewhat higher than the 2 mm reported for sealant liquid and membrane odour traps in previous studies, and it reveals that the odour trap can perform in adverse conditions without getting clogged. Economics of installation and maintenance aspects of waterless urinals carried out here show that the odour trap evaluated in this study can really be a cost effective alternative.

INTRODUCTION

Waterless urinals facilitate collection of urine from homes and public buildings for productive industrial and agricultural applications, a new paradigm in waste management which is gaining increasing attention. Adopting water conservation technologies that assist in reducing consumption of water for human activities can significantly contribute towards mitigating ecological imbalances created in recent years (Vasudevan 2006). Waterless urinals aid in conserving significant amounts of water and energy in addition to reducing the volume of wastewater (Jönsson et al. 1998). Dry and touch-free operations of waterless urinals reduce the risk of spreading communicable disease from urinals, and also help in reducing odour in restrooms (Bristow et al. 2004).

Owing to an increased emphasis on water conservation efforts, there is renewed interest in toilets and urinals designed to minimize the amount of water being used for flushing. Urine, which is comprised of over 96% liquid, does not require any additional water for flushing (Reichardt 2004). Use of hard water for flushing urinals can further enhance the chance of the formation of struvite deposits in waste water pipe lines, resulting in the reduction of cross section or blockages requiring periodic maintenance and replacement of pipes (Udert et al. 2003a). Although the unpleasant odour from urine occurs due to various volatile compounds present in urine resulting from bacterial metabolism or thermal reactions, the formation of ammonia from the urea present in urine is reported to be one of these important reactions (Troccaz et al. 2014). Therefore, ammonia generated from urine can be used as a good tracer for understanding the issue of odour in urinals.

Hydrolysis of the urea present in human urine is the cause of ammonia generation in urinals (Udert et al. 2003b). The enzyme urease hydrolyses urea into ammonia and carbamate. The latter compound decomposes spontaneously to carbonic acid and a second molecule of ammonia (Mobley & Hausinger 1989). The overall reaction can be written as follows:
formula
1
Odour prevention trap mechanisms fitted to waterless urinals assist in preventing odour developed inside drainage lines emanating into restrooms. A study, conducted by UCLA & BioContractors (2000), shows that ammonia levels in waterless urinals utilising sealant liquid odour prevention traps was comparable to conventional water flush urinals, and is well below the lower human threshold detection level of 20 ppm. The first waterless urinal trap using the sealant liquid method was patented by Mr. Beetz of Austria in 1894. Since, then several models of waterless urinals working on both mechanical and biological means for odour control have been developed, and these are widely being used across the world (Münch & Winker 2009). ‘Eco-Lilly’, a low cost self-constructed waterless urinal having ball floats placed in funnels fixed over a jerry can, is also widely used in rural areas of Africa (Münch & Winker 2009).

In India and across the globe, millions of conventional water flush urinals are presently in operation in schools, institutions and public places. Converting these conventional water flush urinals into waterless urinals would not only lead to saving precious fresh water used for flushing, but also reduce the cost of the operation and infrastructure required for this purpose. However, factors such as initial cost of installation and periodic maintenance of waterless urinals have a very strong bearing on widespread adoption of this technology, especially in developing countries like India, where the availability of sufficient financial outlay is always a cause of concern. Existing design models of waterless urinals are expensive and still require periodic maintenance. An estimate shows that the annual maintenance cost of a single waterless urinal using sealant liquid odour trap technology would range from USD 45 to 120 (Stumpf 2006). However, studies related to the performance of waterless urinal odour traps with respect to their odour control efficiency are almost non-existent as most waterless urinal designs come under the patent regime. This study explores the performance of a non-patented low cost waterless urinal functioning with a membrane-type odour trap already being marketed in India.

MATERIALS AND METHODS

In the present study, odour control efficiency of a low cost membrane-based waterless urinal odour trap, which is not patented and is manufactured by Shital Ceramics in India, was chosen for evaluation (Figure 1). The membrane of the odour trap, which is made up of low density polyethylene, is in the form of a flat tube having open ends on both sides. The membrane of the trap is housed inside a circular pipe with its top end firmly fixed to a conical shaped holder, which guides urine to flow into the membrane, while the other end is loosely suspended inside the circular odour trap body. The circular odour trap body extends beyond the length of the membrane and finally contracts into a conical shaped end for fixing to a wastewater drain pipe. A bell-mouth adapter on top of the circular odour trap body enables fixing of the odour trap to the outlet of urinals at the bottom.
Figure 1

Picture of a membrane-type odour trap manufactured by Shital Ceramics in India. The picture shows a conical shaped attachment with membrane mounted, which is placed inside the odour trap body, having a bell mouth for enabling fixing of the odour trap below urinal outlets.

Figure 1

Picture of a membrane-type odour trap manufactured by Shital Ceramics in India. The picture shows a conical shaped attachment with membrane mounted, which is placed inside the odour trap body, having a bell mouth for enabling fixing of the odour trap below urinal outlets.

Odour control experiments

Conducting odour control studies of waterless urinal odour traps installed in functional urinals posed several challenges. Therefore, in this study, in experiments 1–4 the odour trap chosen was fixed to an outlet on top of a covered urine storage tank to estimate its ammonia odour control efficiency, and in experiments 5–7 the odour trap was fixed to a urinal pan connected to a wastewater drain to study ammonia control efficiency. In experiments 1–4, concentrations of ammonia measured above the outlet of the storage tank before fixing the odour trap were used as control. A 16 litre capacity storage tank with a removable lid was used to store 1, 5, 10 and 15 litres of urine in the four experiments conducted. The odour trap was firmly fixed to the outlet of the storage tank before ammonia measurements were taken in experiments 1–4. In experiments 5–7, a normal urinal pan without an odour trap was connected to a wastewater drain of a urinal block for control measurements, and a urinal with an odour trap was connected to the same waste drain to estimate its odour control efficiency. Measurements were taken on three different occasions to get a general trend. In these experiments, ammonia measurements were taken over the openings in the urinal pan.

Gas detection tubes No.3L (Gastec Corporation, Japan) were used for measuring ammonia concentration in the range of 0.2 ppm to 78 ppm. Corrections for temperature and pressure have been considered for all the measurements as recommended by the manufacturer. The coefficient of variation for ammonia measurements using the gas detection tubes are up to 10% for 1 to 10 ppm and 5% for 10 to 30 ppm.

Resistance to clogging experiments

The standard procedure prescribed in ANSI Z 124.9-2004 (ANSI 2004) was used to conduct the resistance to clogging experiment of the odour trap used in the study. For this purpose, the odour trap used in the study was installed to a urinal pan mounted on a wall. An arrangement for continuous flow of water for flushing the urinal pan was also installed. The experiment, conducted by placing cigarette butts of length 38 ± 2.5 mm at regular intervals and flushing with water, was repeated for a total of five times after removal of cigarette butts deposited in the urinal pan at the end of each cycle of the experiment. Initially two unfiltered cigarettes were placed in the urinal and water for flushing at a flow rate of 0.5 litres per minute was continuously released. Subsequently, the cigarette butts placed in the pan were alternated between normal unfiltered butts and crumpled unfiltered cigarette butts during the tests. During each cycle of the experiment, a total of twenty cigarette butts and 5 litres of water for flushing the urinal were used.

Particle flow experiments

To determine the maximum size of particle that can pass through the odour trap, experiments used stone grit particles of specified size, which were placed in the urinal and flushed with water at a flow rate of 0.5 litres per minute for 10 minutes. Based on existing literature, particles of 1, 2, 3 and 4 mm (±0.15 mm) size were used and the experiment conducted in triplicate (Münch & Winker 2009). The experiment, which is considered to have begun the moment a particle placed in the urinal pan is washed inside the odour trap, was continued until a particle placed in the urinal pan emerged out of the odour trap or up to a maximum duration of 10 minutes. Water used for flushing was collected in an open container, covered with a white filter cloth, kept below the urinal pan and disposed of whenever it was full. The white filter cloth used helped in identification of particles emerging out of the odour trap during the experiments. The resistance to clogging and particle flow analysis experiments are standard tests conducted to analyse performance of odour traps under adverse user behaviours usually witnessed in urinals.

RESULT AND DISCUSSIONS

Odour control

The concentration of ammonia measured during experiments 1–4 conducted after fixing the odour trap over the outlet of a 16 litre storage tank with varying quantities of urine are given in Table 1. Ammonia concentrations measured in the four experiments conducted were 0.44, 1.31, 0.66 and 0.88 ppm for 1, 5, 10 and 15 litres of urine stored in the tank, respectively. However, control measurements taken at the outlet of the tank, without fixing odour traps for all the quantities of urine stored in the tank, exceeded the maximum measuring range of 78 ppm of the ammonia gas detection tubes 3 L used in the study. A minimum reduction of over 98.3% of ammonia gas concentration from the storage tank was observed after the odour trap was installed directly over the outlet in all four experiments conducted.

Table 1

Ammonia odour control efficiency of the low-cost membrane based waterless urinal odour trap

Experiment No.Quantity of urine stored in the tank (litres) aAmmonia measured at outlet fixed over the covered urine storage tank (control measurement in ppm)bAmmonia leakage from the odour trap fixed at the outlet of urine storage tank (ppm)Ammonia control efficiency of the odour trap (%)c
>75 0.44 >99.4 
>75 1.31 >98.3 
10 >75 0.66 >99.2 
15 >75 0.88 >98.9 
 Average 0.8  – 
 Standard deviation 0.4  – 
 CV (%) 45.1  – 
Experiment No.Quantity of urine stored in the tank (litres) aAmmonia measured at outlet fixed over the covered urine storage tank (control measurement in ppm)bAmmonia leakage from the odour trap fixed at the outlet of urine storage tank (ppm)Ammonia control efficiency of the odour trap (%)c
>75 0.44 >99.4 
>75 1.31 >98.3 
10 >75 0.66 >99.2 
15 >75 0.88 >98.9 
 Average 0.8  – 
 Standard deviation 0.4  – 
 CV (%) 45.1  – 

aStored urine from large tanks was transferred 5 min before the experiments into small 16 litre capacity experimental tank.

bAmmonia measured exceeded the measuring range of gas detection tubes (Gastec No. 3 L) used for measurements.

cEfficiency has been calculated using control measurement (75 ppm) as reference, therefore the actual efficiency will be higher than the value given.

Table 2 shows the results obtained in experiment nos. 5–7 in which the ammonia measurements were taken in a normal urinal without an odour trap and a urinal with an odour trap, both connected to the same wastewater pipe on three different occasions. Ammonia concentrations of 2.6, 3.48 and 3.93 ppm were measured for a normal urinal without an odour trap, while it was found to be reduced to 0.22, 0.33 and 0.22 ppm, respectively, in the urinal fitted with an odour trap connected to the same wastewater pipe. A minimum reduction of 90.5% in the ammonia odour was found in these experiments. The minor variations observed in the amount of ammonia leaking from the odour trap could be due to the improper sealing of the membrane when a particular measurement was taken.

Table 2

Ammonia odour measurements for (i) a normal urinal and (ii) a waterless urinal working with the odour trap evaluated in this study, both connected to the same waste water drain of a urinal block

Experiment No.Ammonia measured at outlet of normal urinal pan without an odour trap (control measurement in ppm)Ammonia leaked from waterless urinal pan fixed with odour trap (ppm)Ammonia control efficiency of the odour trap (%)
2.6 0.22 91.5 
3.48 0.33 90.5 
3.93 0.22 94.4 
Average 3.3 0.3 92.1 
Standard deviation 0.7 0.1 2.0 
CV (%) 20.3 24.7 2.2 
Experiment No.Ammonia measured at outlet of normal urinal pan without an odour trap (control measurement in ppm)Ammonia leaked from waterless urinal pan fixed with odour trap (ppm)Ammonia control efficiency of the odour trap (%)
2.6 0.22 91.5 
3.48 0.33 90.5 
3.93 0.22 94.4 
Average 3.3 0.3 92.1 
Standard deviation 0.7 0.1 2.0 
CV (%) 20.3 24.7 2.2 

The results obtained in the present study are comparable to values reported by UCLA & BioContractors (2000) and Larson (2002) using liquid-based sealant waterless urinals in the USA. In a study conducted in normal urinals and waterless urinals working on sealant liquid-type odour traps, the mean concentrations of ammonia observed were 0.40 and 0.52 ppm inside the urinal bowls (UCLA & Biocontractors 2000). Some individual measurements reported in the study were as high as 1.00 ppm. Larson (2002) reported that the ammonia concentration in waterless urinals is barely detectable and the values are comparable to normal water flush urinals. Although the authors reported non-detectable levels of ammonia for most test samples, a few measurements taken at the urinal lip level exceeded 2 ppm.

The study also confirms that ammonia levels in the closed system of waterless urinals can be significantly higher. The concentration of ammonia in stored urine at elevated pH is reported to reach as high as 8,100 ppm (Udert et al. 2006). Therefore, stagnation of urine, particularly due to clogging of urinal pans or drainage lines, can result in high amounts of odour in restrooms. According to the Occupational Safety & Health Administration (2003), the federal agency of United States of America which enforces safety and health legislation, the short-term (15 minute) exposure limit for ammonia is 35 ppm. Although most public urinals in India are in a bad state due to poor maintenance, occurrence of serious health hazard due to ammonia does not occur due to factors such as urination by men in standing posture with their nostrils at a distance from the urinal pan, ventilation arrangements in urinals and use of urinals for relatively very short duration.

Resistance to clogging

The odour trap used in the study did not exhibit clogging during the experiments conducted to determine its resistance to clogging. However, occasional variation in the quantity of water flowing out of the odour trap was observed during the experiments. This could be due to tobacco particles released from the cigarette butts hindering the flow of water through the passage above the membrane. Examination of the odour trap after five successive cycles of the experiment revealed the presence of a few tobacco particles held inside the membrane. In the US market, as per the federal law, waterless urinals are only allowed to be sold if there is evidence of non-clogging during resistance to clogging tests conducted with cigarette butts (ANSI 2004). However, in addition to cigarette butts and other objects dumped in urinals, accumulation of sludge from urine including struvite precipitated in the odour traps over time can affect the performance of waterless urinals. Also, the performance of both sealant-liquid and membrane-based odour traps is reported to be affected by the accumulation of sludge over a period of time (Münch & Dahm 2009). Accumulation of sludge in the odour traps will require periodic maintenance and also replacement of components of the odour traps. The membrane trap used in the study has to be replaced on such events (Chawda 2014). However, the problem of sludge accumulation can be reduced both by disciplined use of urinals by the users, such as not putting in unwanted particles like bubble gum, cigarette butts, spitting residues of oral tobacco products and Betel nuts used for chewing, and undertaking periodic cleaning routines of the urinals and odour trap components.

Particle flow

Grit particles up to 4 mm in size were used in the experiments conducted to assess the optimum size of particles that can flow through the odour trap. Time taken by particles to pass through the odour trap varied significantly from 1 to 30 seconds, therefore a specific time range could not be specified from the results of experiments conducted in triplicate. Particles up to 4 mm in size pass through the odour trap. However, the average time taken by large-sized particles was significantly higher, as they came into contact with the sides of the membrane, which restrained its movement inside the membrane. The size of particles that can flow through the odour traps is governed by the size of the openings in the urinal pan and the membrane used in the odour trap, whereas the time taken by them to do so depends on various factors like the density of the particles, the position of the particle in the odour trap and friction encountered with the components of the odour trap, apart from the velocity of the water flow. The significant difference in the time taken by particles to pass through the odour trap observed in the experiments confirms this effect. Münch & Dahm (2009) reported that membrane traps such as the one-way valve (Keramag) and curtain valve made of liquid silicon rubber (Addicom) allow passage of grit up to 2 mm in size.

Economics of waterless urinal odour traps

The prices of popular waterless urinal models available in India collected through a market survey as part of this study is given in Table 3. In the study, the prices of all the different types of waterless urinal models were collected. As all the waterless urinal models surveyed are more expensive than the low-cost odour trap evaluated in the present study (INR 750 or USD 12.0), the nearest comparable model being marketed by Parryware (INR 11,750 or USD 187.0) has been chosen for a comparative analysis (Table 4). The waterless urinals being marketed by Parryware are based on the widely used sealant liquid odour trap technology. However, the advantage of the odour trap evaluated in the study is that it costs only INR 250 (USD 4.0) and it can also be used for retrofitting existing water flush urinals. Retrofitting an existing water flush urinal into a waterless urinal functioning with sealant liquid odour traps requires complete replacement of the existing urinal pan at a cost of INR 11,750 per urinal pan (USD 187) (Chawda 2014). Also, the maintenance cost of a sealant liquid based waterless urinal works out to be INR 4,100 per urinal per annum (USD 65.3) for 50 uses per day (Chawda 2014). However, for the same number of uses, urinals functioning with the membrane-based odour traps used in the study only need to be replaced twice a year at a total cost of INR 500 per urinal (USD 8.0) (Sompura 2014). Stumpf (2006) reported that the annual maintenance cost of a sealant liquid based waterless urinal trap would range from USD 45–120 in the USA. Therefore, it can be concluded that the odour trap evaluated in this study is cost effective in terms of installation and maintenance aspects. Such cost effective systems assist in wider installations of waterless urinal technology in public places and institutions where sufficient funds are not available.

Table 3

Prices of popular waterless urinal models available in India

S. NoWaterless urinal brandTechnology usedProduct Reference No.Cost of one complete set of waterless urinalImportant maintenance featuresa
CERA Membrane Trap 5004 INR 11,480 (USD 182.7) 
Duravit Sealant Liquid Trap (cartridge free trap) 84436 INR 70,455 (USD 1121.4) 
Falcon Sealant Liquid Trap Flax ST 2255 INR 22,000 (USD 350.2) B,C 
Hindware Sealant Liquid Trap (cartridge free trap) 60017 INR 23,920 (USD 380.7) 
Kholer Sealant Liquid Trap (cartridge free trap) Steward K-4918 INR 43,100 (USD 686.0) 
Parryware Sealant Liquid Trap Ecotrap INR 11,750 (USD 187.0) B,C 
Sunming Non-Return Valve N.A. INR 16,500 (USD 262.6) 
Uridan Sealant Liquid Trap Admiral INR 16,500 (USD 262.6) B,C 
Shital Membrane Trap N.A. INR 750 (USD 11.9) 
S. NoWaterless urinal brandTechnology usedProduct Reference No.Cost of one complete set of waterless urinalImportant maintenance featuresa
CERA Membrane Trap 5004 INR 11,480 (USD 182.7) 
Duravit Sealant Liquid Trap (cartridge free trap) 84436 INR 70,455 (USD 1121.4) 
Falcon Sealant Liquid Trap Flax ST 2255 INR 22,000 (USD 350.2) B,C 
Hindware Sealant Liquid Trap (cartridge free trap) 60017 INR 23,920 (USD 380.7) 
Kholer Sealant Liquid Trap (cartridge free trap) Steward K-4918 INR 43,100 (USD 686.0) 
Parryware Sealant Liquid Trap Ecotrap INR 11,750 (USD 187.0) B,C 
Sunming Non-Return Valve N.A. INR 16,500 (USD 262.6) 
Uridan Sealant Liquid Trap Admiral INR 16,500 (USD 262.6) B,C 
Shital Membrane Trap N.A. INR 750 (USD 11.9) 

aAbbreviations: A – Membrane trap to be replaced periodically; B – Sealant liquid to be refilled periodically; C – Cartridge of the trap to be replaced periodically; D – Non-return valve to be replaced periodically.

Table 4

Economics of installation and maintenance of waterless urinal odour traps

DescriptionMembrane based waterless urinal odour trap evaluated in this study (Shital)aSealant liquid based waterless urinal odour trap (Parryware)b
Mechanism of operation Flat LDPE membrane prevents odour Liquid seal prevents odour 
Cost of a new system Cost of urinal pan – INR.500/- (USD 8.0)
Cost of trap is INRs.250/-(USD 4.0) 
Cost of entire system – INR.11,750/- (USD 187.0) 
Replacement of parts Complete set of odour trap has to be replaced Periodic refilling of sealant liquid and annual replacement of cartridge is required 
Maintenance cost INR 500 (USD 8.0) (trap to be replaced at least once in six months) INR 4,100/- (USD 65.3) (Sealant liquid INR 3000/- (USD 47.7) and Cartridge INR1100/- (USD 11.5) annually for urinals with 50 uses per day) 
Maintenance routine involves Trap has to be dismantled from urinal and waste pipe (a) Liquid seal replacement for every 1000 uses 
  (b) Replacement of cartridge once a year 
Time required for maintenance/replacement of odour trap 30 minutes 10 minutes 
Retrofitting of existing urinals Traps can be installed in existing urinals Complete set of new urinal pans capable of housing odour traps have to be installed 
Issues/Constraints Supply of odour traps by manufacturer Supply of cartridge and sealant liquid by the manufacturer 
DescriptionMembrane based waterless urinal odour trap evaluated in this study (Shital)aSealant liquid based waterless urinal odour trap (Parryware)b
Mechanism of operation Flat LDPE membrane prevents odour Liquid seal prevents odour 
Cost of a new system Cost of urinal pan – INR.500/- (USD 8.0)
Cost of trap is INRs.250/-(USD 4.0) 
Cost of entire system – INR.11,750/- (USD 187.0) 
Replacement of parts Complete set of odour trap has to be replaced Periodic refilling of sealant liquid and annual replacement of cartridge is required 
Maintenance cost INR 500 (USD 8.0) (trap to be replaced at least once in six months) INR 4,100/- (USD 65.3) (Sealant liquid INR 3000/- (USD 47.7) and Cartridge INR1100/- (USD 11.5) annually for urinals with 50 uses per day) 
Maintenance routine involves Trap has to be dismantled from urinal and waste pipe (a) Liquid seal replacement for every 1000 uses 
  (b) Replacement of cartridge once a year 
Time required for maintenance/replacement of odour trap 30 minutes 10 minutes 
Retrofitting of existing urinals Traps can be installed in existing urinals Complete set of new urinal pans capable of housing odour traps have to be installed 
Issues/Constraints Supply of odour traps by manufacturer Supply of cartridge and sealant liquid by the manufacturer 

aData based on manufacturer of membrane traps Shital Ceramics, Gujarat, India.

bData based on manufacturer of sealant liquid based waterless urinals Parryware, India.

CONCLUSIONS

Over 90.5% reduction in ammonia gas reduction was observed in the experiments conducted using the low-cost membrane based waterless urinal odour trap evaluated in this study. The results obtained are comparable to previously reported values in the literature for sealant liquid based odour traps. In addition, no clogging was observed in the resistance to clogging tests conducted. Particles of up to 4 mm passed through the membrane-based odour trap, which is higher than the previously reported value of 2 mm for all types of odour trap. The installation and maintenance costs of the membrane trap are also much lower compared to the widely used waterless urinals functioning with sealant liquid odour traps. The membrane-based odour trap also can be effectively used for retrofitting existing water flush urinals into waterless urinals at much lower cost, unlike the sealant liquid-based odour traps, which requires a complete replacement of the existing urinal system.

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