Cost analysis of decentralized wastewater treatment system
Cost analysis of the decentralised waste water treatment system is crucial and important. Figure 7 shows the cost analysis conducted by (Kuttuva, Lele & Mendez 2018), they plotted the curve treatment cost vs. number of units. Figure shows three curves red curve, black curve and dotted points. Red curve indicates the power law curve, black curve indicates the engineering cost and dotted points indicates the actual values.
Where, R is the risk involved, L is the hazard and C is the consequences.
Utilisation of sewage is very important and can enhance the environment strength. Due to the difficulties in transportation of the sewage in the centralised system the focus is getting transfer to decentralized system. In decentralised system sewage can be treated in the nearby site of the waste water treatment, this was not possible in case of centralised waste water treatment. This advantage of decentralised waste water system over the conventional centralised system makes it popular. This decentralised treatment of waste water is also environmental friendly and economic.
Glaciers of Himalayas are the great resource of fresh water but due to worldwide temperature alteration and environmental change, these glaciers are subsiding and liquefying at a quicker speed and this straightforwardly prompts a risk. This increased flow rate of water can be the reason of floods in the lower depth areas, but for long duration of time this can also cause a problem of low water supply (Zhang et al., 2009). Ground water that used to be revived by melt water during summer will also get influenced.
The meaning of grey water is different in different research papers. The most widely recognized one is that, grey water is all indoor unit wastewater produced from kitchen sink, dishwasher, wash bowl, shower, clothing machine, cleaning water etc. (Jefferson et al., 2004). It is not quite the same as that supposed to be grey water that contains wastewater from toilets. In a few examinations, grey water obtained from kitchen sink and dishwasher is rejected and is not considered. In this manner that wastewater is more homogeneous in its substance and is less difficult to treat. The grey water studied in this work, cover a more extensive scope of sources, including open offices, organizations, wide range of administration enterprises, for example, auto washers, spa and so forth close to family units. All things considered, regardless of where it is produced. To put it clearly, grey water can be characterized as, streams leaving urban building, barring can water. In family units, dish, shower, sink, and clothing water include 50-80% of the aggregate wastewater. Since grey water is less polluted and has less contamination than mechanical wastewater, it is less difficult to treat and reuse compared to the waste water coming from the mechanical industries. It is a reasonable contender for reuse, in light of the fact that it is easily available and accessible on location for reuse (Winward et al., 2008). To utilize the recycled water for non-consumable purposes is generally safe from a health point of view, and it could be superior to anything utilizing tap water from a quality point of view, ex. utilizing grey water which contains nutrients like N and P for water system.
Advantages of decentralized wastewater treatment system
Considering this, the decentralized wastewater treatment generally requires little volumes and pipes of small diameters. This type of work is normally claimed by non-government elements. Most on-location and group frameworks release the utilization of soil; this is generally utilized for individual family and also for a small community. Further available unutilized waste water can be utilized again for flushing or gardening work, people are normally open, glorified to serve this generous piece of work (Booz & Rocky Mountain Institute, 2004).
The main advantage of using grey water is reducing the use of available drinkable water. This can be achieved by refining the grey water with the help of waste water management systems. This step is very much helpful in the urban areas. Reutilization of the grey water during the conduction of Olympics in the Beijing, China was very economical and profitable (Zhang et al. 2009). As during the Olympics, requirement of the fresh water was high and to fulfil this requirement, management of Olympics and Beijing, China comes with different ideas of reutilizing grey water. These ideas are listed below,
- Recycling of grey water
- Better treatment of grey water
- Recycling of the rainwater
- Developing plants for treatment of the small scale work
One can solve the problem of drinkable water by implementing the above listed steps. But utilization of these steps depends upon the different factors like, availability of grey water, size of the plant and requirement of the drinkable water. (Arora, Yadav & Saroj 2016) concluded that one can increase the efficiency of the plant by choosing an appropriate technology. A study was finished by (Nhapi, 2004) for neighbourhoods and he demonstrates that the grey water generally contains large quantity of nitrogen, but he also stated that quantity of phosphorus is also high and one has to solve this also. The disadvantages comes with the decentralized frameworks of waste water is that, very harsh rule have to be followed while conducting the reutilization of grey water work. These risks can be overcome by following the strict rules (Verstraete, Caveye & Diamantis, 2009).
(Zhang & Tan 2010) developed a decentralized wastewater management technique for an urban area in Bejing, China. They found that ecological sanitation (EcoSan) is comparatively good approach for wastewater management and does not have any pitfalls. They found that EcoSan is less expensive in sense of material and energy expenditure. Figure 1 shows the treatment procedure conducted and RBC (rotating biological contractors) equipment utilized by them. Below figure has four parts, top left and top right are primary segregation tank and four-class rotating biological discs respectively. While in the bottom left and right parts, lamella separator and sand filtration tank are fitted. They found that above technique can help in reduction of short ROI (return of investment) and unit investment capability.
Definition and importance of grey water
(Sharma & Vairavamoorthy 2009) conducted study on urban water management. They reviews different techniques and tools and also analysed different urban water demand management (UWDM) measures. The measures of UWDM are categories in three sets, technical & structural, socio-political and financial & economic. They concluded that financial gains can be achieved by using different UWDM measures. UWDM can help in water crisis and water loss management.
(Oakley, Gold & Oczkowski 2010) targeted their study towards the control of nitrogen using wastewater decentralized treatment. They analysed different process performance and alternative strategies. They utilized pre-anoxic, post-anoxic and simultaneous nitrification denitrification processes as shown in figure 2. They conducted reliability and stability analysis of different decentralized wastewater techniques and found that most of the techniques are not able to match the 50% probability standard.
(Massoud, Tarhini & Nasr 2009) targeted their study towards decentralized wastewater treatment and management. Figure 3 shows the most disposal and treatment techniques utilized for wastewater treatment while figure 4 shows the process of selecting the most appropriate technique. They also stated that training program of the employees should be conducted for proper working and maintenance of the different equipment. They also concluded that proper planning can help in overcoming the challenges of wastewater treatment.
(Jenssen 2005) conducted decentralized of urban grey water treatment at Klosterenga oslo. They analysed urine and faecal for fertilizer and potentially energy production, by analysing nitrogen, phosphorus and faecal coliforms content. (Furumai 2008) conducted their study to use the rainwater and wastewater for sustainable utilization. They analysed all strategies and techniques and concluded that sustainable use of grey water is very potential. (Fattahi & Fayyaz 2010) developed a mathematical model for the analysis of wastewater utilization. They considered different factors like satisfaction of consumers who uses urban water, social problems and benefits to nation. Their work-objectives were reduction in the leakage water, reduction in the cost of water distribution and level of social satisfaction. To analyse the efficiency and performance of developed model they considered Hamedan potable water network. They found that model developed by them can be utilized effectively for the integrated urban water utilization.
(Ahmed & Arora 2012) studied the suitability of the grey water utilization as decentralized alternative water supply option for integrated urban water management. They proposed a new method for grey water re-cyclization shown in figure 5. They reviewed all the strategy of grey water re-cyclization utilized at commercial scale and found that constructed wetland, intermittent sand filter and septic tank are the best techniques which are simple in maintenance and operation and are also very cost effective.
Challenges and strategies of decentralized wastewater treatment
(Chirisa et al. 2017) conducted analysis on the decentralization of wastewater in the developing country (Harare, Zimbabwe). They found that while doing the wastewater decentralization in the Harare one have to overcome the environmental challenges. They also concluded that one should consider the social and economic issues. (Barton & Argue 2009) conducted their study on integrated urban water management for residential areas. They developed a reuse model for the maximum use of the wastewater. Figure 6 shows the model developed by them. Model developed by them can be utilized either in small area or in large area. Model developed by them is marginally expensive compared to the conventional model.
Literature conducted reveals that lot of work has been done in the utilization of wastewater or grey water. There are many techniques by which one can reuse the wastewater or grey water. Most of the literature conducted is focused on the decentralization of the wastewater management for the developing countries.
- Research question, Aim/objectives and sub-goals
From the above literature review it has been found that, decentralization of wastewater management has lots of potential. Project focuses on the following research questions:
- To find out a systems for reutilizing grey water and rainy water
- To maximise the use of available qualities and resources in grey water
- To lessen the utilization of available drinking water with water obtained from decentralized waste water systems
- To quantify and solve different challenges given by environmental conditions.
- To develop a decentralized waste water management, that is cheap and produces more output.
Present work targets towards the improvement in the development of a decentralized system for grey water. Targets of present work are to reduce the effective cost, increase the overall output. Present work also targets to minimize the risk and disadvantages associated with decentralized waste water management. Challenges given by environment are also considered in the present work for proper utilization of the wastewater.
The present study has been further divided into small sub-goals listed below.
- Sub-goals 1:
To conduct a case study on how the decentralized waste water management syste have been used to reutilize the grey water during the Olympics. How the water resources have been utilized will also be studied and analysed.
- Sub-goals 2:
To examine the different risks, those can influence the performance of the decentralized waste water treatment system. Different safety factors will also be identified and solved for performance enhancement.
- Sub goals 3:
Future aspects of the decentralised waste water management systems related to urban areas will be analysed.
- Methodology
During the Olympics Beijing, China developed decentralised waste water management system for effective utilization of the grey water to fulfil the requirement. They developed a plant which can purify 10000 litres of water on daily basis. After utilizing the decentralised waste water treatment in Beijing, the outcomes indicated that, this technique is not financially economic as it requires high amount of costs as far as grey water use. So they developed a plant which can reutilize grey water as well as water collected during the rainy seasons (Zhang et al. 2009).
Studies on wastewater utilization
In the present work grey water has been utilized as main source for the decentralised waste water management system. Rain water has also been utilized in the present work. First the grey water and rain water is collected than it has been used. Efficiency of the system has been determined with considering different safety and environment factors. As grey water is not in pure form its limitation has also been discussed in the present work. Cost of the overall set up has also been analysed and changes has been done for decrement in the overall cost of the decentralised waste water management system. Risk analysis and management has also been conducted in the present work by considering different hazards due to the nature and other factors.
In this section of different types of elements found in the grey water are discussed. First the municipal grey water is collected. After the collection of grey water, test has been conducted and from the test it has been found that the municipal grey water contains different product listed in the table 1. These products have been listed with their cost in euros. Cost in euros has been represented on per kilogram or per m3 basis.
Table 1 shows all the products found in the municipal grey water. Grey water mainly consist the deposits like nitrogen and phosphorus. One can see that the extractions of these components can be very helpful (Nhapi, 2004).
Table 1 Potential product recovery from municipal water (Nhapi, 2004)
|
Potential product recovery from municipal used water |
|
|
Water (H2O) |
1 per m3 sewage |
|
€ 0.250 / m3 cost |
|
|
0.25 total per m3 sewage |
|
|
Nitrogen ( N2 ) |
0.05 per kg sewage |
|
€ 0.215 / kg cost |
|
|
0.01 total per m3 sewage |
|
|
Methane ( CH4 ) |
0.14 per m3 sewage |
|
€ 0.338 / m3 cost |
|
|
0.05 total per m3 sewage |
|
|
Organic fertilizer |
0.10 per kg sewage |
|
€ 0.20 / kg cost |
|
|
0.02 total per m3 sewage |
|
|
Phosphorus ( P ) |
0.01 per kg sewage |
|
€ 0.70 / m3 cost |
|
|
0.01 total per m3 sewage |
Test performed on the grey water from the households reveals that, grey water have components like, food scrap, cooking oils, detergent, kitchen waste, shampoo and soap etc.
Table 2 below shows the characteristics of the grey water.
Table 2 Characteristics of the grey water
|
Parameter |
Raw Grey Water |
|
pH (mg / L) |
6.5 – 6.8 |
|
Sulphate (mg / L) |
10 – 50 |
|
Ammonia (mg / L) |
1 – 10 |
|
Turbidity (NTU) |
20 – 100 |
|
Suspended solids (mg / L) |
10 – 100 |
|
Phosphorus (mg / L) |
0.5 – 5 |
|
BOD (mg / L) |
50-150 |
|
TOC (mg / L) |
50-100 |
|
Conductivity (μs / cm) |
150-500 |
Fields of application of grey water
- Cooling tower
- Fire extinguisher
- Gardening
- Toilet flushing
- Irrigation
- Technologies for grey water treatment
- Needs of consumers or users
- Cost of the investment
- Cost of the maintenance
- Space availability
- Planned site
- Risks comes with grey water reutilization
There are different kinds of risk that one has to solve before going for actual practice. These risks include transportation of grey water, availability of grey water, sources of grey water (household or industrial) etc.
Performance of the grey water can be enhanced by using the (rotating biological contractors) RBC (Zhang & Tan, 2010). Table 3 shows the performance of grey water, to analyse the performance of grey water different parameters like TSS, BOD, COD, total bacterial, coliform, turbidity, ammonia and TP were analysed (Zhang & Tan, 2010).
Risk involved due to the hazards in the decentralization of the waste water can be characterised by (Dominguez-Chicas & Scrimshaw, 2010),
Conclusion
R=L×C
|
Table 3 Performance of grey water with RBC (Zhang & Tan, 2010) |
||||||||
|
Parameter (mg/l) |
04 / 12 / 2002 |
18 / 12 / 2002 |
Quality standard for sweeping |
Quality standard for flushing |
||||
|
Inlet |
Outlet |
Removal rate |
Inlet |
Outlet |
Removal rate |
|||
|
TSS |
65.0 |
2.0 |
97 % |
22.0 |
0.5 |
98 % |
5.0 |
10.0 |
|
BOD |
86.2 |
3.0 |
97 % |
123.0 |
1.8 |
99 % |
10.0 |
10.0 |
|
COD |
132.0 |
12.9 |
90 % |
200.0 |
14.1 |
93 % |
50.0 |
50.0 |
|
Total bacterial |
4.7×103 |
320.0 |
90 % |
3.6×103 |
2.0 |
100 % |
– |
– |
|
Coliform |
2.8×105 |
92.0 |
93 % |
2.4×105 |
4.0 |
100 % |
3.0 |
3.0 |
|
Turbidity |
48.0 |
2.0 |
96 % |
74.0 |
1.0 |
99 % |
5.0 |
10.0 |
|
Ammonia |
7.7 |
0.9 |
89 % |
6.4 |
0.5 |
92 % |
10.0 |
20.0 |
|
TP |
5.4 |
2.8 |
48 % |
4.0 |
5.2 |
-30 % |
– |
– |
Risk involved in the decentralization of waste water management system is divided into two categories, one is technical risk and another is external risk.
Technical risks:
This type of risk can be due to the skills of the employee. This type of risk is may also be due to the inefficiency of the equipment used in the decentralised waste water management system.
External risks:
These types of risk involve, employees doing overtime work and can be terrible for the health of the employee. Health of the individual employee is very important as it affects the efficiency and performance of the overall decentralised waste water management system.
Conclusion
In the present work utilization of grey water to make it drinkable has been discussed in detail. Present work is mainly focus on the reutilization of grey water and rain water. In the present work a case study on Beijing, China is also presented which shows the advantages of reutilization of grey water in the urban areas. From the study it has been found that reutilization of grey water is very effective as it helps in reducing the grey water quantity, less utilization of drinkable water and also in enriching the nearby environment. Study shows that decentralization of waste water management is very effective and risk free. Study also reveals that decentralization of waste water management is cost effective, easy to handle and simple when compared with conventional centralised waste water management system. Study also reveals that waste water can be further reutilize with marginal increment in the overall cost of the system.
References
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Ahmed, M., & Arora, M. 2012, ‘Suitability of Grey Water Recycling as decentralized alternative water supply option for Integrated Urban Water Management’, IOSR Journal of Engineering, vol. 2, no. 9, pp. 31-35.
Barton, A. B., & Argue, J. R. 2009, ‘Integrated urban water management for residential areas: A reuse model’, Water Science and Technology, vol. 60, no. 3, pp. 813-23.
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