KENYA STANDARD  KS 2767 -
5:2021  
ICS ##.### 
1st  Edition  
  
 © KEBS  2021   
 Wastewater treatment plants — Part 5: 
Lagooning processes  
 
 
 TECHNICAL COMMITTEE REPRESENTATION  
The following organizations were represented on the Technical Committee:  
1. CSI International ltd  
2. Dousglobal Management solutions  
3. Ecosave Africa Ltd  
4. Embu Water and Sanitation Company LTD  
5. Environment Institute of Kenya  
6. Green Kenya Investment Corporation  
7. Jomo Kenyatta university of agriculture and technology  
8. KenGen PLC  
9. Kenya Chemical Society  
10. Kenya water Institute  
11. Kenyatta university  
12. Nairobi City Water and Sewerage Company  
13. National Environment Management Authority  
14. National Public Health Laboratory  
15. Synergy Ltd  
16. Taita Taveta University  
17. TANATHI Water Works Development Agency  
18. United States International University -Africa  
19. Kenya Bureau of Standards — Secretariat  
REVISION O F KENYA STANDARDS  
In order to keep abreast of progress in industry, Kenya Standards shall be regularly reviewed.  Suggestions 
for improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standards, 
are welcome.  
© Kenya Burea u of Standards, yyyy 
Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 130 of 2001 of  the Laws of Kenya, copyright 
subsists in all Kenya Standards and except as provided under Section 25 of this Act, no Kenya Standard pr oduced by Kenya Bureau of 
Standards may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in  writing 
from the Managing Director.KS 2767 -5:2021  
 
Wastewater treatment plants — Part 5: 
Lagooning processes  
Kenya Bur eau of Standards, Popo Road, Off Mombasa Road,  
P.O. Box 54974 - 00200,  Nairobi, Kenya  
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 kenya bureau of standards (kebs)   KS 2767 -5:2021  
Foreword  
This Kenya Standard was prepared by the Water and Sanita tion Technical  Committee under the guidance of 
the Standards Projects Committee, and it is in accordance with the procedures of the Kenya Bureau of 
Standards  
During the preparation of this standard, reference was made to the following doc ument (s):  EN 12255 -5 :  
Wastewater treatment plants — Part 5: Lagooning processes.  
Acknowledgement is hereby made for the assistance derived from this (these) source (s)  
The parts of these series are as follows:  
– Part 1: General construction principles  
– Part 3: Preliminary treatment  
– Part 4: Primary settlement  
– Part 5: Lagooning processes  
– Part 6: Activated sludge processes  
– Part 7: Biological fixed -film reactors  
– Part 8: Sludge treatment and storage  
– Part 9: Odour control and ventilation  
– Part 10 : Safety principles  
– Part 11: General data required  
– Part 12: Control and automatization1)  
– Part 13: Chemical treatment  
– Part 14: Disinfection1)  
– Part 15: Measurement of the oxygen transfer in clean water in activated sludge aeration tanks  
– Part 16: Physical (mechanical) filtration1)  
 
 KENYA STANDARD  KS 2767 -5:2021  
 
 © KEBS  2021   
 Wastewater treatment plants — Part 5: Lagooning processes  
1 Scope  
This Standard specifies the performance requirements for the installation of lagooning processes.  
This part applies to wastewater lagooning processes tre ating municipal wastewater from combined or 
separate sewerage systems and when used as a tertiary treatment  
NOTE: Lagooning processes are especially suitable for treatment of wastewater where large variations in flow are experienced (e.g. 
resulting from st ormwater).  
2   Normative references  
This Standard incorporates by dated or undated references provision from other publications. These 
normative references are cited at the appropriate places in the text and the publications are listed hereafter. 
For dated r eferences, subsequent amendments to or revisions of any of these publications apply to this 
Standard only when incorporated in it by amendment or revision. For undated references the latest edition of 
the publication referred to applies.  
KS 2766  Wastewater  treatment - Vocabulary  
KS 2767 -1 Wastewater treatment plants - Part 1: General construction principles  
KS 2767 -3 Wastewater treatment plants - Part 3: Preliminary treatment  
KS 2767 -6 Wastewater treatment plants - Part 6: Activated sludge process  
KS 2767 -10 Wastewater treatment plants - Part 10: Safety principles for the construction of wastewater 
treatment plants  
KS 2767 -11 Wastewater treatment plants - Part 11: General data  
3   Definitions  
The definitions given in KS 2766 apply . In addition, for the purpose s of this standard, the following definition 
also applies:  
3.1 
maturation pond  
wastewater lagoon used as tertiary treatment, typically for the removal of pathogenic micro -organisms by 
exposure to solar radiation by competition and predation mechanisms  
4  Process description  
4.1 Natural lagoons  
Natural lagooning for wastewater treatment is designed as a cascade of singular ponds operated 
consecutively. The first pond may be either a settlement or anaerobic pond. The following pond is partly 
aerobic (facultativ e pond) and serves for the degradation of carbon and nitrogen. Subsequent ponds serve for 
advanced treatment including the reduction of pathogens and/or organisms by exposure to solar radiation.  
4.2  Aerated lagoons  2 © KEBS  2021  – All rights reserved  
 Aerated lagoons consist of at least two singular ponds, one with artificial air supply by technical devices 
and the second for sedimentation.  
4.3  Polishing ponds  
Polishing ponds are mainly used for the further reduction of suspended solids in wastewater received 
from treatment plants.  
4.4  Comb inations with other systems  
A combination of ponds and small technical systems (e.g. trickling filter, rotating disc) may be installed in 
cases of overloaded lagoons or where there is a need for advanced treatment. Where odour is likely to 
occur Imhoff tan ks may be installed instead of anaerobic lagoons.  
Screening should be carried out before the wastewater enters aerated lagoons. Additional preliminary 
treatment may be required (see KS 2767 -3). 
5    Requirements  
5.1 General  
The requirements specified in KS 2 767-1 and KS 2767 -10 apply to this part.  
Where technical aeration is a requirement reference should be made to KS 2767 -6 and where additional 
preliminary treatment is required, e.g. screening, reference should be made to KS 2767 -3. 
5.2 Siting  
Where odour i s likely to occur (e.g. natural lagooning) plants shall be located a minimum of 200 m from 
any habitation. The main wind direction, topography, ground water table, geotechnical conditions, risk of 
flooding and landscape should be taken into account.  
5.3 Accessibility  
It shall be possible to bring machinery to any point around a lagoon for the maintenance of banks, control 
of vegetation and de -sludging.  
Unauthorized access to the lagoon installation shall be prevented, e.g. fences.  
5.4 Design  
5.4.1  Process considerations  
The design of the lagooning system shall ensure it operates with all the earth basins full to the top water 
level. If not otherwise agreed, the conditions of operation which prevent damage to the structures shall be 
specified.  
In addition to  the requirements specified in KS 2767 -1 and KS 2767 -11, the following parameters shall be 
considered for the design of a lagooning system:  
a) the climatic conditions for the lagoons treating wastewater under mainly naturally established 
conditions e.g. anaer obic lagoons, facultative ponds, oxidation ponds, maturation ponds. Information 
on the climatic conditions shall be specified;  
 
b) a minimum depth of 1 m taking account of the volume to be occupied by the sludge before withdrawal 
and free sedimentation of sol ids; especially for settlement and anaerobic lagoons:  
 
c) inlet and outlet configuration with respect to sludge blanket level and accessibility for cleaning;  
 
d) the frequency for sludge removal;  
 KS 2767 -5: 2021  
© KEBS  2021  – All rights reserved  3 
 e) the type, number and unit size of aeration equipment for the wate r depth and the protection of the 
bottom from erosion in aerated lagoons;  
 
f) the minimization of short circuiting by suitable shape, design and location of the lagoon inlet and 
outlet;  
 
g) avoidance of floating debris from moving from one chamber to another by use of a siphoning pipe  
placed not more than 1/3 of the depth of the chamber.  
 
h) the intensified growth of algae and their effect on the receiving waters shall be considered;  
 
i) the way of sludge disposal;  
 
j) the effect of storm water.  
5.4.2   Watertightness  
Earth basins shall be watertight to a permeability factor of less than 10 -8 m/s to 0.3 m soil. Other basins with 
short detention time of no more than 10 days and treating secondary effluent e.g polishing ponds shall be 
watertight to a permeability factor of at least 10 -7 to 0.3 m soil. Validation of watertightness should be carried 
out in accordance with national procedures.  
Where watertightness is to be ensured by soil compaction, the optimum compacting conditions e.g. load and 
moisture content, shall be ass essed by preliminary tests. Watertightness shall be tested by laboratory test 
before filling with water by at least three permeability measurements per basin.  
Where watertightness is ensured by a synthetic lining system, the lining shall be, opaque, abrasi on resistant 
and UV resistant. Special precautions shall be provided to prevent gas accumulation under the lining.  
Synthetic linings should be a minimum of 3 mm in thickness.  
Where watertightness is ensured by clay, the layer should be a minimum of 0.3 m t hickness.  
When emptying lagoons or where there is a rise in the level of ground water, measures shall be established to 
protect the watertight construction.  
5.4.3   Banks  
In natural soil and subsoil the banks above and under water of lagoons should not be s teeper than 1:2. The 
banks of lagoons should be protected against erosion. Aerated lagoons should be especially protected 0.3 m 
below and above the water level where wave action is likely.  
Where banks are covered with a clay layer they shall not be steeper  than 1:3 and measures shall be taken to 
prevent this layer from cracking (e.g. cracking by desiccation).  
5.4.4  Structures and pipeworks  
The inlet to the first lagoon within a system shall be fitted with a device for retention and easy removal of 
floating matter. There should be a bypass facility for each lagoon. The interconnecting channel or pipework 
system between lagoons shall be designed to permit cleaning from the bank and shall prevent deposits and 
floating matter from being conveyed downstream. The outlet of the final basin shall be designed to permit 
measurement of flow and sampling.KS 2767 -5:2021    
 
© KEBS  2021– All rights reserved