Water Engineering: Grey Water Recycling, Treatment & Industrial Use

This report provides a comprehensive overview of grey water recycling within the field of water engineering. It begins by defining grey water and highlighting its potential as a valuable resource, especially in arid and semi-arid regions. The report emphasizes the importance of proper grey water management to prevent negative impacts on public health and the environment. It reviews various treatment methods, including aerobic and anaerobic post-treatment processes, and classifies grey water based on quality and intended use. The report also discusses the industrial and agricultural applications of recycled grey water, noting the importance of adhering to health standards for agricultural use. Finally, the report concludes that grey water management is not only crucial for healthy living conditions but also a significant opportunity for wastewater reuse.

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Abstract
The recycled gray water can be used for activities such as flushing of toilets, irrigations among
other relevant uses. Lack of knowledge and experience in this particular field can be attributed to
the slow progress in the wider and dissemination of water. Management systems of grey water
appear to be blank in some aspects of this technology. In many arid and also in the semi-arid
areas, there has been needed to make good use of the little available water. This has led to the
device of ways of ensuring that used water is recycled and used for other activities. The primary
sources of this water are regarded as potential source. The grey water has been considered the
potential source of this recycled water.
Introduction
In the decentralized sanitation projects that are characterized by low-cost, much focus is put on
the construction of toilet. This is very common in the developed countries. Such projects end to
ignore the issue of grey water completely. It is important to note that comprehensive and
sustainable management systems for sanitation with dry toilet are not achievable if the problem
of grey water is not properly sorted out( Burian and Pomeroy 2010).
The consequences of doing that include negative impacts to the public health and the
environment at large. The activities of the proper management of greywater include a collection
of the grey water treatment and possible reuse if not disposal. Prevention of possible human
contact with this water potentially limits or reduces the transfer of pathogens. Proper treatment of
the grey water impacts the adjacent water bodies positively since it reduces the infiltration of
nutrients that possibly facilitates the process of eutrophication.

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Literature review
Greywater extracts its definition from the cloudy appearance that it possesses. Also, this color is
attributed to its characteristics of being found in between the fresh portable whitewater that is
known to be white incur and also sewage water that is characterized with black color. The grey
water is that wastes water from the showers, washbasins, kitchen, sinks and also washing
machines. The issue of the management of the grey water has obtained several definitions. This
is because wastewater excluding toilet wastes water is gaining use in most of the developed
countries.
In these countries, the improper use of the wastewater is considered to be one of the many
causes of the environmental pollution and also killer diseases. In the modern set up, there has
been recognized that proper use of the grey water can actually lead to the creation of very
potential water sources. This mission can only be achieved in the cases where very high
technology is supported by legal frameworks.
The kitchen water is not normally recommended for applications as grey water., however, do not
include wastewater from the urinals, toilets or bidets. This is basically called black water. The
grey water can be collected from all these sources and then used for other activities such as
flushing of the toilets and garden watering that do not require drinking quality of water
(Boyjo,Pareek and 2013). . There is the scarcity of scientific knowledge in regard to
characteristics of grey water and also perfect systems of treatment that will allow for proper
disposal and reuse of the grey water. The main purpose of this project is to highlight some of the
existing treatment methods, classes of grey water and also uses of the grey water especially in
the sector of agriculture for irrigation.

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Methodology and discussions
Post-Treatment of grey water
The post treatment of waste water is also known as the secondary water treatement.These
operations normally follow after the primary water treatment has been done. They seek to
improve the quality of the water to meet specific requirements for particular uses. The activities
are broadly grouped into two steps.
Aerobic post-treatment
The major reason of this particular technique is simply to facilitate the removal of smaller
particles and fibers to protect the possible infiltration of the pipes after major treatment. These
particles may clog the pipes when they are not properly checked. The system transfers the water
as soon as possible to the systems that assist in the removal of both macro and microorganisms.
The stretch filters are meant to retain those large particles and fibers and also permits the large
particles to move to the next level of treatment.
The filter system is best suited for public facilities in which the primary source of the waste is
handwashing.The water is known to lack food particles. If this kind of filter is used to filter the
water particles that have food particles that will accumulate and become anaerobic and effluent
malodorous. This kind of treatment results in grey bucket grey water and also grey water from
diversion devices.
Anaerobic to aerobic post-treatment.
In the cases where a significant quantity of food wastewater finds its way into the system from
the places such as dishwashers and kitchen sink, this particular option is strongly recommended.

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The installation of this system involves operations that are almost similar to those of the
traditional methods . The treated effluent, however, does not pollute the environment is of better
quality as opposed to the ancient one (Fortier 2010).
Figure1 post treatment of water extracted from (Fortier 2010).
The set upon consist of three stage septic tank that is meant to separate the grease from the
effluent. The separated sludge can then be removed frequently .This can be done after every
fourth year as opposed to what used to be bi-yearly in the past. The outgoing effluent is
considered anaerobic. The final stage is leading to the purified water that is almost near the
portable quality. This option is considered one of the most defective and also simple to maintain
processes. This kind of treatment results in the generation of grey water into the GTS

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Classes of grey water
CLASS Quality objectives
of water
Process of
treatment
Agricultural uses Industrial uses
A Accepted PH of 6-
9;Protozoa
reduction of 6-
log,10 Ecoli of
quantity 100mL
Pathogen
reduction through
tertiary
treatement.Also
enough log
reduction that
give required
parameters of
bacterial level
Drinking water for
livestocks.Fodder
supply to dairy cattle
Road construction
Raw food crops for
human beings that
are exposed directly
to recycled water e.g.
tomatoes.
Road construction
Residential uses
e.g. for washing
machines
Industrial system
that is open.
Public access that
is unrestricted
like golf courses.
B 100Ecoli/100mL
PH range of 6-9
20mg/LBOD
30mg/L of
suspended
particles of solid
matter.
Pathogen
reduction through
secondary
treatment
Drinking water a part
from the pigs, grazing
fodder for the dairy
cattle, grazing and
fodder supply for
goats, sheep and
cattle
Processed food for
human or those
chosen crops that are
not exposed to
recycled water
directly
Used in the
closed system of
industries
Construction of
roads
Public areas that
are restricted like
facilities of sports
C PH range of 6-9
30mg/L of
suspended solids
1000Ecoli/100mL
Pathogen
reduction through
secondary
treatment
Cooked human food
Fodder supply and
grazing of goats,
horses etc.
Construction of
roads
Closed systems of
industries
D 10000Ecoli/
1oomL
PH of 6-9
30mg/L
Secondary
treatment
Nonfood crops like
woodlots and flowers
N/A
Free bucket of grey water
This kind of grey water is considered easily accessible. It can be siphoned and distributed using
buckets before it is allowed to go down the drain. Such activities may include collecting of the

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water used in the washing of the machine or from the sink. In most of the cases, there is no
approval required to use this class of grey water. This water can be used for irrigation of the
gardens, toilet flashings and also washing of the parts of the machine (Keely et al 2015).
The bucketing of such water is considered low risk since the activity involves the use of the low
volume of water that has been spread to different locations. The contamination of soil.is expected
to be as minimal as possible and also the runoff experienced is very minimal. It is commonly
known as kitchen waste water or grey water. It constitutes 15% of the total grey water.
Grey water from diversion devices.
It is also called laundry grey water. It constitutes 30% of the total grey water. This device is
known to divert or directs grey water from a known waste pipe that may originate from the
shower or laundry to the garden and used for sub-surface irrigation. This water cannot be used to
support any other activity. There is no special treatment for this water apart from filtering of the
larger particles that could potentially clog the pipes over time. In addition, there are no
provisions for the storage systems for such wastewater. This device has a system of valve that
diverts this grey water to a sewer in case the system is closed either permanently or temporarily.
Most of the pumped systems come with different sizes that are basically designed for single
fixture use.They are mounted on a wall at a position that is slightly raised with 50mm inlet and
the entire underground fitted with pipes of 100mm diameter (Ravinia et al 2017).
Grey water from GTS
It is also known as bathroom grey water in some cases. This is another step up in the complexity
from a system of diversion. Apart from just filtering the bits that are considered lumpy, the

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system improves the quality of grey water that originates from the showers, baths, and even
laundry. This water is treated to a level that it can be used for irrigation purposes or in the toilet.
The disinfected grey water from the GTS is then pumped into a second tank for storage
purposes. This water can be drained from the storage tank and then used for flushing toilets. This
water constitutes 50% of the grey water. This clearly shows that the number of people bathing is
very many.
Industrial use of grey water.
Grey water can be used even in the untreated state, or it can undergo the process of treatment of
varying degrees depending on the intended purpose. The treatment processes are meant to reduce
the level of disease-causing organisms. The recycled water is used for the industrial purposes
that include public parks, landscapes and also golf course irrigation. Other non-potable
applications include the industrial processes and oil refineries ,cooling of power plants
etc.

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Figure1 cooling plants using recycled grey water from (Ravinia et al 2017).
The industrial processes like water mills and carpet dyes, concrete mixing, toilet flushing all
utilize greywater that has been recycled (Sing et al 2016). The level of odor in the treated water
must be as low as possible. This water should be generally fit for the other intended purpose or
use. The water should be clear with much-reduced torpidity ( Jang et al 2014).
Agricultural uses of water
Figure 2 irrigation using recycled grey water extracted from (World Health Organization 2015).
In the arid and semi-arid places, the gray water that has been recycled is used to support
agricultural activities through irrigation. In most of the large water treatment plants, the
requirements and the composition of treated water is strongly regulated by the country
authorities. These standards however must conform to the health standards that have been set
aside by the health sectors before they are used for agricultural purposes.

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Domestic use of grey water
Drinking water is treated under very stringent conditions. Although researchers have pointed out
the present of micro plastics in the bottled water, their consequences have remained to be very
minimal.
Treated grey water that has been recycled is used in other activities like washing, bathing among
others.
Conclusion
The management of the grey water should not only be viewed as a pre-condition for healthy and
clean living conditions but also as a potential means of getting wastewater reused. The treated
water in the decentralized places is used for different operations in the whole world. In the recent
years, there has been the emergence of the use of the treated greywater for agricultural purposes.
This practice is common, especially in the semiarid places (World Health Organization 2015).
The practice can be attributed to the fact that there has been a scarcity of water in these places
for irrigation, the high cost of the artificial fertilizer, so the grey water is seen to possess some
traces of manure, the high cost of the treatment of water among other factors

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References
Boyjoo, Y., Pareek, V.K. and Ang, M., 2013. A review of greywater characteristics and
treatment processes. Water Science and Technology, 67(7), pp.1403-1424.
Burian, S.J. and Pomeroy, C.A., 2010. Urban impacts on the water cycle and potential green
infrastructure implications. Urban ecosystem ecology, (urban ecosystem), pp.277-296.
Fortier, P.A., 2010. Detecting and estimating rectification of gap junction conductance based on
simulations of dual-cell recordings from a pair and a network of coupled cells. Journal of
theoretical biology, 265(2), pp.104-114.
Jang, H.M., Cho, H.U., Park, S.K., Ha, J.H. and Park, J.M., 2014. Influence of thermophilic
aerobic digestion as a sludge pre-treatment and solids retention time of mesophilic anaerobic
digestion on the methane production, sludge digestion and microbial communities in a sequential
digestion process. Water Research, 48, pp.1-14.
Keely, S.P., Brinkman, N.E., Zimmerman, B.D., Wendell, D., Ekeren, K.M., De Long, S.K.,
Sharvelle, S. and Garland, J.L., 2015. Characterization of the relative importance of human‐and
infrastructure‐associated bacteria in grey water: a case study. Journal of applied
microbiology, 119(1), pp.289-301.
Ravinia, R., Girotto, F., Peng, W., Cossu, R., Pivato, A., Raga, R. and Lavagnolo, M.C., 2017.
Effect of aerobic pre-treatment on hydrogen and methane production in a two-stage anaerobic
digestion process using food waste with different compositions. Waste management, 59, pp.194-
199.

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Sing, D.K., Fortney, J.J., Nikolov, N., Wakeford, H.R., Kataria, T., Evans, T.M., Aigrain, S.,
Ballester, G.E., Burrows, A.S., Deming, D. and Désert, J.M., 2016. A continuum from clear to
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World Health Organization, 2015. Sanitation Safety Planning: Manual for Safe Use and
Disposal of Wastewater Greywater and Excreta. World Health Organization.