DESIGN OF A DECENTRALISED WASTEWATER TREATMENT PLANT FOR NYARI ESTATE

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1 UNIVERSITY OF NAIROBI SCHOOL OF ENGINEERING DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING DESIGN OF A DECENTRALISED WASTEWATER TREATMENT PLANT FOR NYARI ESTATE REG NO.: F21/17272/2010 NAME: MBUCHI EMMANUELLA GATHONI SUPERVISOR: DR. F.N. GICHUKI

2 INTRODUCTION Wastewater management is comprised of wastewater collection, treatment, and reuse or disposal of effluent and sludge (Crites and Tchobanoglous, 1998). It is essential for several reasons: (1) Protecting public health and the well-being of the communities; (2) Protecting the water resources and the environment; and (3) In water-scarce regions, for reuse purposes in order to reduce the pressure from the potable resources (Bakir, 2001; Friedler, 2001).

3 DEFINITION OF DECENTRALISED WASTEWATER SYSTEM (DEWAT) A decentralized waste water system (DEWATS) is an onsite or cluster wastewater system that is used to treat and dispose of relatively small volumes of wastewater, generally from individual or groups of dwellings and businesses that are located relatively close together

4 ADVANTAGES OF DEWATS The recycled water can be re-used It can enhance the property value of an area Simple technologies can be used as compared to central waste water treatment plants They are less expensive to construct and operate than centralized systems and in some cases are less expensive than individual sewage systems

5 STATEMENT OF THE PROBLEM AND PROBLEM ANALYSIS Kenya s real estate market is quickly growing with more and more estates coming up on the outskirts of Nairobi which need waste water treatment facilities. The residents of these estates are forced to have their own individual septic tanks since establishing an individual connection to a municipal waste water treatment (WWT) facility is expensive in terms of infrastructure costs. These septic tanks are also managed individually and hence may present an environmental challenge since the effluent is not monitored to see if it satisfies the NEMA disposal standards.

6 Literature Review STAGES OF TREATMENT 1. Preliminary Treatment 2. Primary Treatment 3. Secondary Treatment 3. Tertiary Treatment

7 SITE ANALYSIS Area of site: 3, m 2 Area covered by treatment plant: m 2 Highest point -1767m Lowest point -1751m

8 Overall objective To design a decentralized wastewater treatment facility (DEWAT) for Nyari Estate. Specific objectives 1. Determine the quantity and quality of waste water. 2. Propose the path of wastewater conveyance. 3. Design the components of the wastewater treatment system

9 STATEMENT OF SCOPE Determine quantity Determine quality Propose a conveyance path Design the treatment plant components

10 GENERATION OF CONCEPT Problem Identification Data collection Assessment of alternative methods Design of components Performance of system in pollutant removal

11 DEWAT SYSTEM COMPONENT LAYOUT two chambered settler Anaerobic Baffle Reactor (ABR) Horizontal Flow Roughing Filter

12 METHODOLOGY

13 Objective 1: Quantity and quality of wastewater QUANTITY OF WASTE produced was based on; Current Population Projected population based on 20year design time P t = P 0 (1+GR) n Peak Factor, PF = 18+ P 4+ P Average wastewater produced per day = 85% of daily water demand Peak Flow = PF x Average daily wastewater produced

14 WASTEWATER DISTRIBUTION OVER THE DAY Source:

15 QUALITY OF WASTEWATER Treated Waste Content NEMA Disposal Standards (mg/l) BOD5 30 COD 50 SS (suspended solids) 30

16 Objective 2: Propose conveyance System Outline of road network Proposed conveyance system V = 1 n R2/3 S 1/3

17 Objective 3: Design of components

18 SETTLER 1st chamber; Length = 2/3 x 8.76 = 5.84m 2nd chamber; Length = =2.92m Total volume of settler = volume of settler + sludge volume = = m3 Depth of settler = W= 2.92m Total volume of settler Area of settler = = 0.82m 1.0m

19 ABR Reactor Working Volume, V w = 357m 3 Compartment up flow area, A u =28.33m 2 Total compartment area = 37.77m 2 Reactor width, r w = 7.71m Reactor length = 15.42m Actual length of each up flow chamber = 2.32m 1. Design HRT (Hydraulic Retention Time) =42 hours for start-up 2. Number of compartments, N = 6 3. Peak up flow velocity = V p = 0.54m/h 4. Compartment width to length ratio C W:L = 3 5. Reactor depth, r D = 3m 6. Compartment up flow to down flow area ratio R U:D = 3 7. Hanging baffle allowance =, d h = 0.2 (Source: K.M. Foxon and C.A. Buckley)

20 HORIZONTAL FILTER V F = Q 1.5m/h Vd = 1.5m/h H W = Q A Qd L1+L2+L3 W = 0.3 to = 0.3 to E = Ce Co = e - L L 1 = 2-4m, take as 4m L 2 = 1-3m, take as 2m L 3 = 1-2m, take as 1m Depth (H) = 1.2m Width, W = 5.9m L 1 + L 2 + L 3 = 5m - 7m Depth should be between 0.8 to 1.2 m d g1 = 12-18mm d g2 = 8-12mm d g3 = 4-8mm

21 RESULTS PARAMETER Method/Formula Result QUANTITY OF WASTEWATER Quantity of wastewater (daily) Peak Daily Wastewater Population x (85% of daily water consumption per capita) PF x Daily wastewater PF= PF = 18+ P 4+ P CONVEYANCE OF WASTEWATER 51m 3 /d 204m 3 /d Slope of first pipe (225mm Diameter) Slope of second pipe (450mm Diameter) Slope of third pipe (800mm Diameter) V = 1 n R2/3 S1/ V = 1 n R2/3 S1/ V = 1 n R2/3 S1/

22 SETTLER Sludge produced per year Sludge per capita per day(0.1l) x 365 x Population (400) 14.6 m 3 Area required 0.5 x Wastewater volume/day 25.5m 2 1 st chamber 2 2 nd chamber 1 Total volume of settler 3 x Total length 5.84m x Total length 2.92m 3 [Minimum retention time (3hrs) x m 3 Average wastewater flow per hour] + sludge volume Depth Total volume of settler Area of settler 1.0m

23 ABR Reactor Working Volume, V w Design up-flow velocity, vd F x HRT 24 Vp = m 3 0.3m/h Compartment up flow area, A u Total compartment area F Vd x 24 A u x (1+RU:D) RU:D 28.33m m 2 Reactor width, r w Reactor length, r L Actual length of each up flow chamber Vw x CW: L N x rd N x rw CW: L [ 2 x x 0.2 ] m 15.42m 2.32m

24 HFRF(Horizontal Flow Roughing Filter) Filtration Flow, V F Q = 0.3 to 1.5m/h A = 7.08m 2 H W Height 1.2m Width 5.9m Length ABR efficiency BODin BODeff BODin BOD eff = BOD in e ktt 7m 84.4% K t = K 20 X (Tave-20) Filter efficiency SSo SSc SSo SS c = SS o [ (HLR)] 86.34% HLR = Q As

30 CONCLUSION The quantity and quality of the wastewater produced in the estate were determined which assisted in selecting the most appropriate treatment method to be used. Components of the system were then designed. The first component designed was a two chambered settler. An anaerobic baffle reactor was the next component to be designed. Tertiary treatment takes place in a horizontal flow roughing filter. The overall objective was achived

31 RECOMMENDATIONS Investigate the effect of adding more chambers to the ABR Incorporate the settler and ABR into one unit to save of space The treated effluent can be used to irrigate lawns. This can be done through sub-surface irrigation hence, evergreen lawns. The methane produced from anaerobic digestion in the ABR can be collected and used as energy. The sludge can undergo treatment and drying to make fertilizer

32 REFERENCES Syed R. Qasim Waste water treatment plant Planning, Design, and Operation ", Benefield, L.D., And C.W. Randall, "Biological Process Design Of Waste Water Treatment", Prentice - Hall, Englewood Cliffs, N.J Metcalf and Eddy, 1991 Wastewater Engineering - Treatment, Disposal, and Reuse McGraw-Hill, Inc., New York. U.S. EPA, 1993 Combined Sewer Overflow Control Manual EPA-625R Gavle, Darrel R., and David G. Mitchell, 1995 Innovative and Economical SSO Treatment Utilizing Fine Screens and Chlorination Presented at the EPA National Conference on Combined Sewer Overflows, Washington, D.C. Hartmann, L., (1999), Historical Development of Wastewater Treatment Processes, In: J. Winter (Ed), Environmental Processes I, wastewater treatment. Weinheim: WILEYVCH. Couture, M., J. Lamontagne, and B. Gagne, John Meunier, Inc.; O. Dalkir, Cegeo Technologies; and C. Marche, University of Montreal; Abstract of a presentation at the New York Water Environment Association, New York, NY

33 REFERENCES Mara, D. Sewage Treatment in Hot Climates, A Wiley Interscience Publication, John Wiley and Sons. Neptune Pacific Ltd., On-site and Small Community Sewage Management with the N- DN Biofilter Treatment Plant FOXON K, DAMA P, BROUCKAERT C and BUCKLEY C (2001) Design considerations for the implementation of an anaerobic baffled reactor in lowincome settlements in Kwa-Zulu Natal. Proc. of the IWA Conf. on Water and Wastewater Management for Developing Countries, Kuala Lumpur, Malaysia. BARBER WP and Stuckey DC (1999) The used of an anaerobic baffled reactor (ABR) for wastewater treatment: A Review. Water Res. 33 (Orozco, 1997) 1559 BELL J and BUCKLEY C (2003) Characterisation of the methanogenic populations in an operating anaerobic baffled reactor. The International Water Association Conference on Environmental Biotechnology, Advancement on Water and Wastewater: Applications in the Tropics, Universiti Teknologi Malaysia, Johor Bahru, Malaysia OROZCO A (1997) Pilot and full-scale anaerobic treatment of lowstrength wastewater at sub-optimal temperature (15ºC) with a hybrid plug-flow reactor. Proc. of the 8th Int. Conf. on Anaerobic Digestion, Sendai, Japan

34 THANK YOU

U N I V E R S I T Y OF NAI R O BI S C H O O L O F ENGINEERING FEB 540: ENGINEERING DESIGN PROJECT 2014/2015 ACADEMIC YEAR

U N I V E R S I T Y OF NAI R O BI S C H O O L O F ENGINEERING DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING FEB 540: ENGINEERING DESIGN PROJECT 2014/2015 ACADEMIC YEAR PROJECT TITLE: DESIGN OF