Gouda, H. (2014) Urban water security: LCA and sanitary waste
management. Environmental Scientist - Water Security, 23 (3). pp.
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Urban Water Security: LCA and
Sanitary Waste Management
Hazem Gouda describes a case study that aimed to reduce sanitary waste disposal via
WCs and used life cycle assessment to assess the various reduction strategy options.
Option Measure Primary objective
1Install 6 mm screens on storm overflow at
To screen storm overflows to constrain solids larger
than 6 mm or equivalent to comply with minimum
aesthetic pollution requirements for discharges
2‘Think before you flush’ campaigns
To encourage a change in domestic disposal habits to
dispose of sanitary solids via the bin rather than the WC
3Install flow storage To reduce the frequency and volume of overflow spills,
thus reducing the number of SW items discharged to the
4Retrofit stormwater source control
To reduce stormwater entry to the sewer system, thus
reducing the frequency and volume of overflow spills
To limit infiltration to the sewer system, thus reducing
overflow spill frequency and volume
Retrofit outlet chokes on existing WCs and
introduce these to new building developments
To force a change in disposal habits from using the WC
to using the bin through the increased possibility of WC
blockage in the home
Table 1. Options for the management of sanitary solids
water-secure world is one where everyone has
access to safe, affordable water, protected from
oods, droughts and water-borne diseases.
Urban water security means that urban water systems
should not have negative environmental effects, even
over a long time perspective, while providing required
services, protecting human health and the environment,
and minimising the use of scarce resources.
FLUSHING OF SANITARY WASTE PRODUCTS
The ushing of sanitary waste (SW) items via water
closets (WCs) has undermined urban water security
in a number of developed countries. The presence of
WCs and fully sewered systems has eased the disposal
of a range of items, with the WC being used as a
‘rubbish bin’. Sanitary waste items disposed of via the
WC comprise female sanitary items including sanitary
towels, panty liners, tampons and applicators, and
general bathroom refuse such as cotton buds, baby
wipes and condoms.
An investigation of people’s opinion about the disposal
of SW items has shown that the practice of ushing is
due to convenience and perceived hygiene. In the UK it
is estimated that about 700,000 panty liners, 2.5 million
tampons and 1.4 million sanitary towels are ushed via
the WC every day. The total contribution of SW to total
sewer solids load varies and depends on water supply,
cultural habits, way of life and level of development.
SW causes technical problems for the sewer network
(e.g. deposition and blockage) and aesthetic problems
when the waste nds its way through the combined
sewer overows (CSOs) in combined sewer systems.
The CSOs normally operate when the sewer system
is running under full capacity during heavy rainfall
storms; then the wastewater will be released to the
aquatic environment. In the UK about 70 per cent by
total length of sewerage systems are combined, and
these systems typically have CSOs.
CASE STU DY: LIFE CYCLE ASSESSMENT AND SW
The case study presented in this article addresses
SW management and actively presents solutions that
address the challenges to urban water security. The
case study has been carried out under the SWARD
(Sustainable Water industry Asset Resource Decision)
project funded by the UK Government and the UK
water industry. The case study demonstrates a wide
variety of efcient and effective strategies for reducing
SW disposal via WCs.
The study has estimated the amount of SW that enters
the sewer systems for a catchment in Scotland. A
detailed hydraulic model was used to simulate the ow
in the sewer system and estimate the annual amount of
SW escape to the aquatic environment from CSOs and
sewer overows (SOs) during heavy rainfall storms.
The data from the hydraulic model are needed for
the life cycle assessment (LCA) component of the
study. LCA is a technique that can be employed to
determine energy, mass ows and environmental
burdens for a number of sewer-related options for
handling SW. LCA can help to direct decision-makers
20 | environmental SCIENTIST | October 2014
October 2014 | environmental SCIENTIST | 21
Figure 2. Interactions between LCA stages.
Figure 1. Fushing profiles for study catchment, think before you flush (TBYF) campaign and retrofit campaign showing
(A) Number flushed/year (B) Average weight (t)/year of sanitary waste.
The catchment is located on the coast of Scotland and
has 626 domestic properties with a population of about
1,500. The ‘system’ is formed by the sewerage system
from the household WC to the wastewater treatment
plant (WTP) and its outfalls. The catchment isserved
by 80 per cent combined sewers and 20 per cent surface
water sewers. The network has an internal CSO, a storm
outfall at the treatment plant and an emergency outfall.
SW ENTERING THE SEWER SYSTEM
The amount of SW that enters the sewer system was
estimated based on population, number of women
and their age, and number of babies in the town. Data
regarding the average number of items used per person
per day were available from the surveys conducted
prior to the ‘think before you ush’ (TBYF) campaign.
towards the more sustainable/preferred investment
solution, and the transparency of the process can help
demonstrate to stakeholders that decisions made are
as environmentally sound as possible. LCA is one of
the tools commonly in use for products and services
to assess the environmental impacts on environmental
systems and/or compare energy use, pollutant
emissions and impacts between proposed alternatives.
CATCHMENT DESCRIPTION AND MANAGEMENT OPTIONS
The case study presented here was conducted as part of a
EPSRC-funded project that developed a decision support
system to assist water service providers to include
sustainability in their asset management planning
processes. Six proposed options used in the case study
for the management of SW are presented in Table 1.
interpretation. The interactions of the four main LCA
phases are represented diagrammatically in Figure 2.
The study has been carried out in order to evaluate
the environmental consequences of six different
alternatives for SW management for a particular
catchment. The goal of the study was to evaluate the
resource consumption, pollutant emissions and the
consequential environmental impacts of alternative
SW management options and scenarios during
their operation period, in a European context. The
boundaries that are set for the options must be identical
if a comparison is to be considered. In this study the
materials, energy, natural resources, transportation,
use and disposal were analysed.
Table 3 gives an overview of the material used for
the SW management options. Data from specic
manufacturers of the products implemented for each
option and data from the SimaPro database were
utilised where data for the specic process were not
available. Waste streams are generated at each phase
of the life cycle and waste management, including the
mechanisms for treating, handling and transport of
waste prior to release into the environment. Sensitivity
analysis was carried out for the waste scenario for the
different options. The main life cycle stages include
three phases and their related boundaries are shown
in Figure 3.
The environmental indicators selected for this case
study included carbon dioxide (CO2), sulphate (SO4),
nitrogen oxides (NOx) and sulphur dioxide (SO2)
emissions and energy use. The results are presented
in this section according to the functional unit, which
is emissions per kilogram of gross solids reduction
The population data presented in Table 2 were obtained
from the census that represents the catchment at the
time of the study. The prole of the SW entering the
system for the study catchment is shown in Figure 1.
THINK BEFORE YOU FLUSH CAMPAIGN
The TBYF campaign was run in the catchment along
with collection of social survey data. The survey
data from running the campaign (option 2) shows a
reduction of 65–70 per cent in the total amount of SW
entering the system. The SW input data from the TBYF
campaign, shown in Figure 1, has been used for this
option or when it is combined with any other option.
RETROFITTING TO CONSTRICT WC OUTLETS
For the retrot option (6) it is assumed that, although
sanitary towels will not be ushed, 15 per cent of
certain other SW items will still be ushed, resulting
in 681.435 kg of SW entering the system per year, as
shown in Figure 1.
The SW prole data for each option was used along
with the detailed hydraulic model to estimate the total
weight of SW escape from the sewer system to the
aquatic environment via CSO/SO.
LIFE CYCLE ASSESSMENT
LCA is a technique involving cradle-to-grave
analyses of production systems or services and
provides comprehensive evaluations of all upstream
and downstream energy inputs and multimedia
environmental emissions. The International
Organization for Standardization outlined the
methodological framework for conducting LCA in four
phases: goal and scope denition, inventory analysis,
impact assessment, and improvement analysis and
Women aged 18—59 Women aged 12—17 Children 0—4 Total population
Total No. 426 35 69 1516
Table 2. Population data
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This involves the designers of sanitary products
liaising closely with sewage undertakers in the design
and procurement phase of their products. Hence, the
way forward towards a secure urban water system is
to manage SW in a sustainable way by encouraging
behavioural change to stop the ushing of such items
and design degradable products.
Figure 3. The elements of life cycle inventory analysis for proposed options.
1. Ashley, R., Blackwood, D., Butler, D., Jowitt, P., Oltean-Dumbrava,
C., Davies, J., McIlkenny, G., Foxon, T., Gilmour, D., Smith, H.,
Cavill, S., Leach, M., Pearson, P., Gouda, H., Samson, W., Souter,
N, Hendry, S., Moir, J., and Bouchart, F. (2002) Making more
sustainable decisions for asset investment in the water industry
– Sustainable Water Industry Asset Resource Decisions – the
SWARD project. In: Strecker, E., and Huber, W. (eds.) Global
Solutions for Urban Drainage. Proceedings of the Ninth
International Conference on Urban Drainage, Portland, Oregon.
ASCE, Reston, VA, USA.
2. Gouda, H., Ashley, R., Gilmour, D., and Smith, H. (2002) Life cycle
analysis and sewer solids. Water Science and Technology, 47(4),
Dr Hazem Gouda is a team member of the International
Water Security Network (IWSN) and programme manager
at the University of the West of England. He is a civil and
environmental engineer with over 24 years of extensive
experience in civil and environmental engineering. His research
is mainly focused on flood risk management, sustainable urban
drainage systems, water resources management, wastewater
engineering and life cycle assessment (email@example.com).
for the proposed options. Table 7 illustrates the SW
results from the hydraulic model for each option and
the relevant environmental emissions per kilogram
of SW prevented from escaping to the environment
during its life cycle.
The results show that the storage tank has the highest
environmental emissions and energy use among all
studied options per kilogram of SW prevented from
escaping to the environment. The TBYF option gives
the lowest energy use and environmental effect as
it has the lowest score among all studied options,
followed by rehabilitation and retrot constricting of
LCA has been used to suggest improvements to the way
in which SW is managed in urban drainage systems and
addresses the challenges to our urban water security.
The results from the SW case study have indicated
that the option of changing user habit can signicantly
reduce the items ushed down WCs and hence reduce
the total amount of SW entering the system.
The LCA results show that the TBYF campaign option,
which is related to habit change, has the lowest
environmental impact per kilogram of SW prevented
from entering the sewerage system. However, one of the
critical aspects is the lifecycle of the sanitary product
itself. It should be possible to design products which
have a strong likelihood of being disposed of via a WC
in such a way that they degrade appropriately and can
be appropriately dealt with by the sewage undertaker.
1. Screen 6 mm rotary drum screen at storm outfall made of stainless steel.
2. TBYF Paper leaflets, questionnaire and posters.
3. Storage tank Concrete tank to store 1100m3 of water.
4. Rainwater barrel Plastic barrels: total of 219 barrels made of polythylene.
5. Rehabilitation Replace 300 mm, 450 mm and 600 mm concrete pipes. Total pipe length 87m.
6. Constricting toilets (WC) Replacing toilet outlet connection with smaller plastic pipes (75 mm dia.) and cistern-flushing
valve to 3 L/flush.
Table 3. The material components used for each of the options.
gas kg CO2
kg SO4 + equ. NOx kg SO2 kg Energy MJ
1Screen 95% 8 0.2067 0.0092 0.1764 127.07
2TBYF 66% 0.56 0.0026 0 0 11.79
3Storage tank 51% 136 1.7188 1.7097 0.3155 1282.27
17% 16 0.0972 0.0080 0.0136 471.32
(i n fi l tr at i on
35% 4 0.0200 0.0106 0.00098 53.10
6Retrofit 94% 2.3 0.0296 0.0153 0.00322 73.16
Table 4. Emissions values per kg gross solids reduction for proposed options