Reference number  
RS 126-4: 2018  
© RSB 2018  
 
 
 RWANDA 
STANDARD  DRS  
126-4 
 
Second  edition  
2018 -mm-dd 
(Reaffirmed 2018 ) 
Wastewater treatment plants  
Part 4: 
General data required  
  DRS  126-4: 2018  
©RSB 2018 - All rights reserved                  ii 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2018  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
Requests for permission to reprodu ce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 788303492  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw   
ePortal: www.portal.rsb.gov.rw   DRS  126-4: 2018  
iii                ©RSB 2018 - All rights reserved  
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ .............  1 
2 Terms and definitions  ................................ ................................ ..... Error! Bookmark not defined.  
2.1 General definitions  ................................ ................................ ..........  Error! Bookmark not defined.  
2.2 Types of wastewater and wastewater collection  .........................  Error! Bookmark not defined.  
2.3 Wastewater quantity and quality  ................................ ...................  Error! Bookmark not defined.  
2.4 Methods, characteristics and Impact on the environment  ..........  Error!  Bookmark not defined.  
2.5 Preliminary and primary treatment  ................................ ................  Error! Bookmark not defined.  
2.6 Fixed film treatment  ................................ ................................ ........  Error! Bookmark not defined.  
2.7 Activated sludge treatment  ................................ ............................  Error! Bookmark not defined.  
2.8 Other wastewater treatment  ................................ ...........................  Error! Bookmark not defined.  
2.9 Sludge treatment  ................................ ................................ .............  Error! Bookmark not defined.  
 DRS  126-4: 2018  
©RSB 2018 - All rights reserved                  iv 
 Foreword   
Rwanda Standard s are prepared  by Technical Committees and approved by R wanda Standards Board (RSB) 
Board  of Directors in  accordance with the procedures of RSB, in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical committees is to prepare national standards.  Final Draft Rwanda S tandards adop ted 
by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and gazettment as 
Rwanda Standards.  
RS 126-4 was prepared by Technical Committee RSB/TC 013, Water and Sanitation  
In the preparation of this standard, reference was made to the following standard:  
BS 12255 -11:2001  Waste Water Treatment Plant —Safety Principles  
The first. edition (RS 126 -4: 2012 has been reaffirmed by the Board on dd -mm-2019 . 
RS 126 consists of the following parts, under the general title Wastewater  treatment plants:  
 Part 1: Vocabulary  
 Part 2: General construction principles   
 Part 3: Safety principles   
 Part 4: General data required  
  DRS  126-4: 2018  
v                ©RSB 2018 - All rights reserved  
 Committee membership  
The following organizations were represented on the Technical Committee on Water and Sanitation  (RSB/TC 
013) in the preparation of this standard. )  
Ministry of Environment (MoE)  
Ministry of Disaster Management and Refugee Affairs (MIDIMAR)  
Ruliba Clays Limited  
Shine Engineers Multisectoral Company Limited (SEMC Ltd)   
Sulfo Rwanda Industries (SULFO)  
University of Rwanda/College of Science and Technology (UR/CST)  
Water and Sanitation Corporation Ltd (WASAC Ltd)  
Rwanda Standards Board (RSB) – Secretariat  
 DRS  126-4: 2018  
1                ©RSB 2018 - All rights reserved  
 Waste Water Treatment Plant — Part 4: General Data Required   
1 Scope   
This Draft Rwanda Standard specifies data which is necessary for the planning, design, bidding, performance 
Guarantees, construction, start -up and compliance testing of a wastewater treatment plant or parts of it. This 
standard gives fundamental information  about the practi ces; this standard has not attempted to specify all 
available practices.  
This standard provides general requirements and processes for wastewater treatment plants for more than 50 
PT. 
2 Normative references  
RS 548 -1:2012: Wastewater treatment –part1– Vocabul ary 
RS 548 -2:2012: Wastewater treatment plants – Part 2: General construction principles  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions apply.  
3.1 
plants  
a new wastewater treatment plant; an upgrading or exten sion of an existing wastewater treatment plant or a 
part of a new or extended wastewater treatment plant (e. g. sludge handling facilities)  
3.2  
clients  
a municipality, city or other organization which intends to build a wastewater treatment plant or parts  thereof, or 
its representative  
3.3  
functional tender  
tender document that contains the design loads, a description of the site where the plant is to be built, the 
relevant discharge limits and any additional requirements  
NOTE  Turn-key contractors design  the plant on the basis of the requirements and plans specified by the client (possibly 
with the assistance of a consulting engineer) and give bids on the plant as a whole in accordance with an overall guarantee. 
The turn -key contractor who secures the con tract is responsible for the construction and the start -up of the plant as well as 
for the compliance with requirements demanded in the tender documents (turn -key project).   
©RSB 2018 - All rights reserved                  2 
 3.4  
sectional tender  
tender documents prepared for different sections of work for a plant  
Note: e. g. earth work, concrete work, mechanical equipment, electrical installations, buildings etc. A plant is normally 
designed by a consulting engineer. Different companies may get the commission ing for the different sections. A consulting 
engineer may be commissioned to coordinate and to supervise the work.  
3.5  
consulting engineer  
an independent engineer commissioned by the client designing a plant or parts of it and/or supervising the 
construction  
NOTE  He may assist the client with any work preparing all or part of the tender documents. He supervises the 
construction and checks the time schedule and costs. The consulting engineer has knowledge and experience in planning, 
design and operational aspects of  wastewater treatment plants.  
3.6  
turn-key contractors  
a contractor building a plant or parts of it as a whole  
NOTE  the turn -key contractor is a company which has knowledge and experience in planning, design, construction and 
operational aspects of waste water treatment plants.  
4 Client options  
The client decides whether a functional tender or a sectional tender shall be prepared.  
The client may commission a consulting engineer to carry out one or more of the following:  
a) establish the design loads and data;  
b) prepare the tender documents for a functional tender;  
c) design the plant and estimate the costs and prepare the tender documents for the sectional tender;  
d) inspect the construction in case of functional tendering;  
e) supervise and coordinate the construction in c ase of sectional tendering;  
f) evaluate the bids on the tenders and to propose which contractor or contractors (in case of sectional  
g) Tendering should be commissioned.  DRS  126-4: 2018  
3                ©RSB 2018 - All rights reserved  
 5 Basic design data required  
Where applicable the following basic data either measured or est imated shall be provided by the client or his 
Representative e. g. consulting engineer.  
5.1 Loading data  
5.1.1  Sewerage system  
The data on the sewerage system should include:  
a) Areas served by combined and/or separate sewers;  
b) Proportions of flows and loads from separate and/or combined sewer systems in dry weather     
c) Conditions;  
d) Storage capacity for storm water within the sewerage system;   
e) Potential to control and balance flows and loads within the sewerage system;  
f) Infiltratio n flows in dry weather conditions and their seasonal fluctuations (where appropriate);  
g) Septic and corrosive components of the wastewater.  
5.1.2  Population served  
The data on the population served shall include:  
a) Current population connected to the sewerage system ; 
b) Population connected at start -up of the plant;  
c) Population connected at design horizon;  
d) Seasonal variations of population (e. g. holiday periods);  
e) Weekly variations of population (e. g. movement of commuting population).   
5.1.3  Significant trades and industries  
A list of trades and industries which discharge significant loads to the sewerage system should include the 
following flows and loads e. g.:  
a) COD, BOD 5, KN, NH 4-N, NO 3-N, total phosphorus, total suspended solids, organic suspended solids,  
b) Salinity and alk alinity; shown as current, start -up, and design target data for:   
©RSB 2018 - All rights reserved                  4 
 c) Hourly peak (m3/h, kg/h);  
d) Weekly peak day (m3/d, kg/d);  
e) Maximum weekly average (m3/week, kg/week);  
f) Annual average (m3/a, kg/a)  
g) In addition, for trades and industries with seasonal fluctuations the periods of high and low loads shall  
be included preferably as an annual diagram.  
h) The client shall specify dischargers who handle hazardous, toxic or inhibitory material and identify  
i) Which precautions are necessary to prevent that hazardous, toxic or inhibitory materials being 
discharged. Organic discharges with low biodegradability should be specified.  
5.1.4  Data from existing wastewater treatment plants  
The loading data and the operational r esults of the existing wastewater treatment plants contain valuable 
information.  
As a minimum the following data for at least the previous year shall be provided:  
a) Annual wastewater flow (m3/a), proportions treated physically, chemically and biologically;  
b) Average quantity (m3/d) and composition of sludge with % solids, and % volatile solids content and      
c) Heavy metals;  
d) Annual quantity of screenings, grit and floatables;  
e) Average volume of liquor from sludge treatment (m3/d) and organic and nutrient content;  
f) Average quantity of digester gas (m3/d); 
g) – Electrical energy produced from digester gas (kWh/a);  
h) Electrical energy consumed (kWh/a);  
i) Probability plots and diagrams showing the following over a year wastewater flows (m3/d) and the daily  
j) Loads of COD, BOD 5, KN, NH 4-N, NO 3-N, total phosphorus, total suspended solids, organic  
k) Suspended solids, salinity and alkalinity;  DRS  126-4: 2018  
5                ©RSB 2018 - All rights reserved  
 l) Seasonal temperature of the wastewater or biological reactor temperatures over a year;  
m) Diurnal fluctuation of the wastewater flow at dry weath er conditions;  
n) Peak flow at storm water conditions (m³/h);  
o) Amount and loads of other wastes than wastewater being delivered to the plant and  
p) Performance of the treatment plant.  
5.1.5  Design flows and loads  
The design flows and loads shall be based on the present flows and loads considering growth or decrease of 
the population, the trades and the industries and future connections of other communities, trades and industries. 
If there are no means to measure th e present flows and loads the design data may be based on the projected 
population. In addition to the population the specific dry weather flow, l/ (population 
 d)????? , a peak factor 
considering storm water and infiltration water and the specific loads i n g/ (population 
 d)????  of COD, BOD 5, 
KN, NH 4-N, NO 3-N, total phosphorus, total suspended solids and organic suspended solids have to be provided. 
Flows and loads of trades and industries should be determined by measurements at the sites.  
The following d esign data should be provided:  
a) Maximum hourly wastewater flow Qmax (l/s) reaching the plant and the probable duration;  
b) Details of discharge limits for storm water e. g. after screening, grit chamber, primary sedimentation or  
c) Other treatment to receiving water or a retention basin;  
d) design peak flow as remaining maximum flow after storm water discharge (l/s);  
e) – Diurnal  (Daily)  variation of the flow at a typical dry weather working day (l/s);  
f) design loads as appropriate for the process in kg/h, kg/d, kg/week  of COD, BOD 5, KN, NH 4-N, NO 3-N,  
g) Total phosphorus, total suspended solids and organic suspended solids as well as the corresponding       
h) Volume of wastewater;  
i) – Minimum daily and weekly ratios of COD/N and COD/P;  
j) In case of seasonal flow and load fluctua tions, day -to-day variation of flow (m3/d) and loads (kg/d) of  
k) The main parameters over a year;  
l) Seasonal temperature of the wastewater over a year;  
m) Annual volume of wastewater (m3/a) and annual loads (kg/a) of COD, BOD 5, KN, NH 4-N, total   
©RSB 2018 - All rights reserved                  6 
 n) Phosphorus, tota l suspended solids and organic suspended solids.  
5.2 Effluent quality, requirements for the disposal of residues and sludge  
5.2.1  Effluent quality  
The requirements of the discharge consent shall be provided. The mode of inspection (e. g. grab samples, 2 -
hour composi te samples, 24 -hour composite samples) and the requirements to meet the consent standard (e.g. 
permitted annual frequency of exceeding consent standard) shall be provided.  
5.2.2  Requirements for storm water overflow discharge  
If there are special requirements fo r storm water to be discharged from the wastewater treatment plant these 
shall be stated.  
5.2.3  Requirements for the residues from preliminary treatment  
The requirements for the disposal of the residues shall be stated,  
e. g. water content of screenings, organic  content of grit, and whether separate or co -disposal of grit, screenings 
and floatable material are permitted.  
5.2.4  Requirements for sludge disposal  
The mode of sludge disposal which is preferred by the client,  
e. g. at agricultural utilization, landfill, inc ineration, coincineration at power stations or other industries, shall be 
stated as well as the appropriate requirements,  
e.g. stabilization, water content. If certain chemicals, (e. g. for mechanical dewatering), are prohibited these 
shall be identified.  
5.3 Site description  
The site description shall include:  
5.3.1  Plans (maps) of the site  
Plans (maps) of the site shall be provided indicating:  
a) Elevation of site;  
b) Contour lines and topography;  
c) Site boundary;  
d) Existing buildings and structures including existing wastew ater treatment plant;  
e) all services including sewers, rising mains, water mains, electrical cables, telephone cables, gas mains  DRS  126-4: 2018  
7                ©RSB 2018 - All rights reserved  
 f) Including information on the capacity (e. g. pressure, voltage, flow);  
g) Service roads (including permissible truck weight) and wal kways;  
h) Access from public road;  
i) Final effluent discharge point with maximum, minimum and average water level of receiving water.  
5.3.2  Existing wastewater treatment plants  
The details of any existing treatment plant shall be described. Plans of layout and struct ures shall be provided. 
The condition of the concrete, service roads and the mechanical and electrical equipment shall be described.  
5.3.3  Ground geology, groundwater and climate  
Borehole information should be provided as follows:  
a) Special characteristics of soil  and ground water including information on possible contamination;  
b) Location of the boreholes;  
c) Ground conditions (e. g. clay, rock, sand);  
d) Maximum, minimum and average groundwater levels.  
e) Climatic information including temperature, humidity, winds etc. shou ld be provided.  
5.3.4  Special site constraints  
Any special site constraints shall be stated and may include the following:  
a) Permissible maximum height of any building or structure;  
b) Limits on odour or noise emissions;  
c) Preservation of groundwater levels;  
d) Preservati on of environment and natural habitat;  
e) Distances of any buildings from site boundary;  
f) Any limits or restrictions on building, transport and operation;  
g) Any special construction material requirements.   
©RSB 2018 - All rights reserved                  8 
 5.4 Additional data required  
The following data required for design should be stated by the client or his representative:  
a) The minimum number of parallel units;  
b) Bypasses;  
c) stand -by equipment;  
d) Requirement for stand -by power supply (kVA);  
e) Any operational parameter (e. g. sludge age, retention time, surface loading, slud ge loading)   specifically 
requested by the client;  
f) Control and automation requirements;  
g) Design service life of equipment;  
h) Truck weight for service roads;  
i) requirements (space and equipment/furniture) for workshops, laboratories, store rooms and offices;  
j) Performance guarantees for:  
1) The plant performance at design load; the testing period in length and time of the year shall be 
stated;  
2) The projected consumption of power and chemicals; testing may be performed together with the 
before  
3) Mentioned testing; thes e tests may be requested for a lower load and/or for another period;  
4) Single units, e. g. screen, mixer, aeration equipment, digester.  
5.5 Time schedule  
a) For a sectional tender all relevant contractual mile stones shall be stated and should include:  
1) starting dat e of contractual delivering time;  
2) anticipated time scale of the start-up and of the commissioning of the plant;  
3) The latest time scale for the contractor to report the construction and/or installations ready for 
inspection and for take over.  DRS  126-4: 2018  
9                ©RSB 2018 - All rights reserved  
 b) For a functiona l tender all relevant contractual mile stones shall be stated and should include:  
1) anticipated starting date of contractual delivering time (notice to proceed);  
2) Time scale for delivering the documents (drawings approval, approval certificate);  
3) Time scale fo r over all functional test (commissioning; commissioning certificate);  
4) Time scale for provisional take -over and final take -over.  
NOTE  Depending on the specific national regulations the client with the help of the contractor should obtain the 
permission for  the planned treatment process and construction work from the authorities prior to the notice to proceed. This 
permission should be obtained before the final contract.  
5.6 Start -up and guarantee testing  
5.6.1  Start -up 
The client may ask for:  
a) Vocational training of personnel;  
b) Advice on the technology.  
5.6.2  Guarantee testing  
If performance guarantees are requested,  it shall be specified how the guarantees are to be tested and who will 
bear the costs. The client may ask for:  
a) Client and contractor perform testing in cooperat ion; 
b) testing performed by a qualified third party in co -operation with the client;  
c) testing performed by a qualified third party in co -operation with the contractor.  
The time frame and the methods for process and plant testing and chemical analysis shall be  specified.  
5.7 Operational cost information  
The client should provide unit costs where appropriate. Examples include:  
a) Personnel costs with indication of trade and skill level;  
b) Electrical energy;  
c) Fuel oil;   
©RSB 2018 - All rights reserved                  10 
 d) Natural gas;  
e) Chemicals (e. g. for phosphate precipitat ion, sludge dewatering and gentrification);  
f) Disposal of residues (screenings and grit) depending on the mode of disposal;  
g) Disposal of sludge depending on the mode of disposal  
6 Documents to be provided by a turn -key contractor or the consulting engineer  
6.1 Com plete documents  
If the information and data provided by the client are not sufficient for the design and the calculation of the costs 
additional information shall be requested:  
a) By contractors immediately after receiving the tender documents or  
b) By a consulting engineer immediately when needed.  
6.2 Design options  
Normally the consulting engineer has to submit several options for which the costs are estimated. A turn -key 
contractor may also submit variants of the same treatment process.  
6.3 Proposed solution  
The offer of a turn -key contractor or the proposed solution of the consulting engineer shall be presented by text 
and drawings in detail in an agreed language. An abstract written for decision makers with no technical 
background should be provided. A list of  abbreviations and symbols shall be attached. The process description 
shall be provided. It shall be explained how process objectives will be achieved.  
The technological and hydraulic calculations including references shall be provided. The relevant design  
parameter for each offered treatment process has to be adequately documented to allow the client to assess 
the proposed process.  
The procedures to ensure how normal operation is maintained during periods of malfunction, break -down of 
equipment and units o ut of operation for maintenance shall be described.  
Within an agreed time scale the following general items (if applicable) shall be presented by text and drawings 
in detail:  
a) Process control system (may be regarded as part of the treatment process), e. g. control panel,  
b) Computer control, sub control stations, instrumentation for process control;  DRS  126-4: 2018  
11                ©RSB 2018 - All rights reserved  
 c) Electrical power system including digester gas engines, transformers, cable arrangement, sub power  
d) Meters, control station, peak power demand (kVA);  
e) Lighting incl uding types and luminous intensity, cables, switches;  
f) Taps and hydrants for service water including the water distribution system as well as the water  
g) Treatment plant if required;  
h) Service roads according to the load;  
i) Walkways;  
j) Workshop, office and storeho use buildings including equipment and furniture as stated in 5.4;  
k) Operating and maintenance manuals.  
The properties of the material for construction and of the equipment installed shall be specified. If not specified 
by the client the procedures for start -up and testing shall be stated.  
6.4 Calculation and presentation of costs  
6.4.1  Construction costs  
Considering the particular conditions of the area and the site, the costs for the complete plant shall be calculated.  
Differentiation shall be made between the costs for civil works (e. g. concrete tanks, houses, and roads), the 
costs for mechanical equipment and the costs for electrical installations including monitoring and process 
control. In addition the costs arising for start -up and guarantee testing shall be sta ted. 
6.4.2  Operational costs  
Considering the particular conditions of the process and the site the annual operational costs shall be presented 
in accordance with flow and load based on the costs and prices as follows:  
a) Personnel costs: based on number and skilled  level required, working in shifts and/or regular working 
time;  
b) Energy costs: to be separately calculated for (where appropriate):  
1) Raw wastewater pumping,  
2) Main treatment process (e. g. aeration, mixers, internal pumping, scrapers),   
©RSB 2018 - All rights reserved                  12 
 3) Tertiary treatment,  
4) Sludge treatment including pumping, mixing, mechanical dewatering,  
5) Miscellaneous (e. g. lighting, heating of buildings); based on the estimated consumption of (where 
appropriate):  
6) Electrical energy,  
7) Natural gas,  
8) Digester gas,  
9) Fuel oil;  
c) Costs for chemicals: to be separately calculated based on the estimated consumption where appropriate 
for: 
1) Primary sedimentation for pre -precipitation and/or flocculation,  
2) Biological reactors for phosphate precipitation,  
3) Biological reactors for denitrification,  
4) Final clarifiers o r filters for phosphate precipitation,  
5) Final clarifiers or filters to improve solids removal,  
6) Sludge to improve thickening,  
7) Sludge dewatering;  
d) Costs for disposal of residues and sludge: to be separately calculated based on the estimated volume or 
mass wher e appropriate for:  
1) Screenings,  
2) Grit, 
3) Grease and floatables and  
4) Sludge;  
e) Costs for maintenance of civil works and equipment shall be separately calculated where appropriate for:  DRS  126-4: 2018  
13                ©RSB 2018 - All rights reserved  
 1) Office buildings, workshops, store houses, laboratories and other non -process buildings,  
2) Tanks and channels exposed to wastewater or sludge,  
3) Pipes exposed to wastewater, sludge or gas,  
4) Plastic tanks and pipes exposed to wastewater, sludge or gas,  
5) Mechanical equipment including spare parts and lubricants,  
6) Electrical equipment includi ng instrumentation and monitoring.  
6.4.3  Presentation of costs  
The client may commission a consulting engineer to estimate the costs. The consulting engineer shall estimate 
the total annual costs for alternatives including capital costs. At sectional tendering t he contractors shall give 
bids on the costs for all items listed in the tender documents. They may offer and state the costs of special 
solutions which are adequate to that described in the tender documents. A turn -key contractor shall give a bid 
on the co sts and as requested in the tender documents. Based on the bids the client shall be able to calculate 
the total annual costs of the plant including capital costs using cost benefit analysis . 
   
©RSB 2018 - All rights reserved                  14 
 BIBLIOGRAPHIE  
[1] Handbook of pollution control, Abbas Ghassemi, Ne w Mexico State University , 2002  
[2] Ministère de l'équipement, du logement et des transports  (96-7TO);  
[3] Conception et exécution d'installations d'épuration d'eaux usées. Fascicule no 81 title II . 
[4] Water resources process and management, V.Bishop, 2001  
 DRS  126-4: 2018  
ICS 13.030.20  
 
 
©RSB 2018  - All right s reserved