Reference number  
DRS 349: 2017  
© RSB 2017 
 
 
 RWANDA 
STANDARD  RS
349
First e dition
2017 -mm-dd
Domestic portable biogas  — Requirements  
 
  DRS 349: 2017  
©RSB 2017 - 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 ascer tain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB 2017  
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or ut ilized 
in any form or by any means, electronic or mechanical, including photocopy ing and microfilm, without 
prior written permission from R SB. 
Requests for permission to reproduce this document should be addressed to : 
Rwanda Standards  Board  
P.O Box 7099 Kigali -Rwanda  
KK 15 Rd, 49  
Tel. +250 252 586103/ 582945  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw   DRS 349: 2017  
iii                ©RSB 2017 - All rights reserved  
 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ ...................... iv 
1 Scope  ................................ ................................ ................................ ................................ ................ 1 
2 Normative references  ................................ ................................ ................................ ....................... 1 
3 Terms and definitions  ................................ ................................ ................................ ...................... 1 
4 Requirements  ................................ ................................ ................................ ................................ ...4 
4.1 General ................................ ................................ ................................ ................................ .............. 4 
4.2 Biogas production  ................................ ................................ ................................ ............................ 6 
5 Fittings  ................................ ................................ ................................ ................................ .............. 6 
6 Sizes ................................ ................................ ................................ ................................ .................. 6 
7 Sampling and criteria for conformity  ................................ ................................ ............................... 7 
8 Marking  ................................ ................................ ................................ ................................ ............. 7 
9 Installation  ................................ ................................ ................................ ................................ ........ 8 
10 Pre-requisites for setting up a portable domestic biogas  ................................ .............................. 8 
 DRS 349: 2017  
©RSB 2017 - All rights reserved                  iv 
 Foreword  
Rwanda Standard s are prepared  by Technical Committees and approved by Rwanda 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 
adopted by Technical committ ees are ratified  by me mbers of RSB Board of Director s for publication and 
gazettment as Rwanda Standards.  
DRS 349 was prepared by Technical Committee RSB/TC 023, Mechanical Engineering and Metallurgy.  
In the preparation of this standard, reference was made to the following standard  (s): 
The assistance de rived from the above source is hereby acknowledged with thanks.  
Committee membership  
The following organizations were represented on the Technical Committee on Engineering and Metallurgy  
(RSB/TC 023) in the preparation of this standard.  
ABEM Engineering and Manufacturing  
AQUASAN  
Chillington Rwanda  
Integrated Polytechnic Regional Cent re - Kigali  (IPRC -Kigali ) 
Master Steel  
Nikil and Consultant  
Rwanda Agriculture Board (RAB)  
Rwanda Environment Management Authority  (REMA)  
Rwanda Utilities Regulatory Authority (RURA)  
SAFINTRA  
SULFO  
Titus and Technology Engineering and Agrotechnology Ltd (TKEA)  
University of Rwanda/College of Arts, Social Sciences  
Rwanda  Standards Board  (RSB) – Secretariat  
  DRS 349: 2017  
1                ©RSB 2017 - All rights reserved  
 Domestic portable biogas  — Requirements  
1 Scope  
This Draft Rwanda Standard covers  the requirements and methods of test for the domestic portable plastic 
biogas used for biogas energy production in home cooking and lighting.  
The standard is not applicable to underground biogas and institutional bio gas. 
2 Normative references  
The following documents are referred to in the text in such a way that some or all of  their conten t constitutes 
requirements of this document.  For dated references, only the edition  cited applies. For undated references, 
the latest edition of the referenced document (including any amendments) applies.  
ISO 1209 -1, Rigid cellular plastics — Determination of flexural properties — Part 1: Basic bending test  
ISO 1209 -2, Rigid cellular plastics — Determi nation of flexural properties  
Part 2 , Determination of flexural strength and appare nt flexural modulus of elasticity  
3 Terms and definitions  
For the purposes of this standard, the follow ing terms and definitions apply . 
3.1 
biogas digester  
simple system which produces biogas, via the natural anaerobic decomposition of organic material  
3.2 
digester /biodigester /bio-reactor /anaero bic reactor  
any water and air tight container designed for the process of anaerobic microbiological degradation of organic 
matter into which the slurry is introduced for digestion and  methanization  
3.3 
stirrer  
mixer  
agitator  
mechanical device inside the digester used to stir the slurry  
3.4 
gas chamber  
space inside or outside the digester for the collection and storage of  biogas   
©RSB 2017 - All rights reserved                  2 
 3.5 
gas bolder retainer  
cantilever beam that holds the gasholder/movable cover in position at the desired biogas  pressure  
3.6 
outlet pipe 
serves as conveyor where the effluent or the slurry is forced out  
3.7 
loading rate  
amoun t of slurry fed per unit volume of digester capacity per day  
3.8 
substrate  
organic material used to produce bio gas  
3.9 
seeding  
adding or introducing anaerobic bacteria to the digester  
3.10 
slurry  
mixture of manure and water  
3.11 
freeboard  
difference in height between the digester wall and the filling line  
3.12 
filling line  
level of slurry when the digesters is  at full load  
3.13 
retention time  
average period that a given quantity of slurry is retained in the digester for digestion  
3.14 
toxic m aterials  
materials that inhibit the normal growth of pathogens in the digester such as mineral ions,  heavy :metals and 
detergents  DRS 349: 2017  
3                ©RSB 2017 - All rights reserved  
 3.15 
metbanization  
digestion  
various processes that take place among the methanogens, non -methanogens and substrates  fed into the 
digester as inputs  
3.16 
metbanogens  
anaerobic  bacteria that act upon organic materials and in the process, produce biogas  
3.17 
collecting tank /inlet  tank 
chamber where substrate and water are collected, stored and separated from heavy and non -biodegradable 
materials before feeding them into the digester  
3.18 
gas production rate  
amount ofbiogas produced per day per cubic meter of slur ry 
3.19 
biogas  
mixture of gas (composed of 50 to 70 % methane and 30 to 40 % carbon dioxide)  produced by methanogenic 
bacteria  
3.20 
scum  
layer of  floating material (mainly fibrous) on the slurry  
3.21 
sludge  
settled portion or precipitate of the slurry; a m ud-like, semi -solid mass  
3.22 
inlet pipe  
serves as conveyor of the substrate -water mixture or slurry from the mixing tank to the digester  
3.23 
gas chamber /gas holder  
space inside or outside the digester for the collection and storage of biogas  
3.24 
effluent 
residue tha t comes out at the outlet after the substrate is digested/processed inside the digester   
©RSB 2017 - All rights reserved                  4 
 3.25 
backfill  
layer of compacted soil and gravel to support the digester wall  
3.26 
mesophilic temperature ra nge 
temperature range of 20°C - 40 °C where mesophilic bacte ria operate  
3.27 
biomass  
biomass is organic material that is plant -based or animal -based, including but not limited to dedicated energy 
crops, agricultural crops and trees, food, feed and fibre crop residues, aquatic plants, alga, fores try and wood 
residu es, organic agricultural, animal and processing by -products, agricultural, municipal and industrial 
organic waste and residues whether or not in landfills, sludge, waste water, and other non -fossil organic 
matter  
3.28 
domestic biogas  
biogas which uses bio mass from 1 household for its own use and consists of a digester and an application for 
cooking, heating or lighting only  
4 Requirements  
4.1 General  
4.1.1  The mixin g tank, digester and gas holder  for portable domestic biogas shall be made either by using 
tank i n HDPE LDDPE,  and laminated woven polyethylene or by plastic container in PVC material . 
4.1.2  The domestic portable biogas shall consist of i nlet/ mixing chamber; d igester (digestion chamber) ; gas 
holder (storage chamber -dome ); outlet; gas conveyance system ; and  slurry compost pit(s)  or any other means 
for collecting the slurry . 
4.1.3  The materials  for moulding shall be of rotational moulded grade and duly stabilized with anti -oxidants 
and shall include black pigments compatible with polyethylene  resin, curi ng agents, catalysts and ultraviolet 
stabilisers. No Fillers s hall be used in the moulding.   
4.1.4 The percentage of carbon black content in the material shall be within 2.0 to 3.0 and its dispersion  of 
carbon black shall be satisfactory  
4.1.5 The materia ls like polyethylene, PVC should be UV treated and thickness of biogas digester shall be 
made of minimum 4.50 mm to 5.50 mm average wall and bottom thickness for digester, Gas  holder, inlet & 
outlet pipe for 2 to 6 m3 capacity Biogas plants and in the ra nge of average thickness from 6.6 mm to 8.2 mm 
for 6 to 10 m3 capacity biogas plants  with provision of inlet and outlet pipe of the same size . 
4.1.6 Wherever, water jacket is provided, the thickness of water jacket should be at least 4.40 mm.  
4.1.7 Biogas holder  shall be made of 4.40 mm average minimum thickness with provision for outlet 
connections and higher thickness for higher capacity biogas plants as mentioned above under  4.1.6 . 
4.1.8 The PVC container shall be  fitted over the steel frame work and hel d firmly against it . DRS 349: 2017  
5                ©RSB 2017 - All rights reserved  
 4.1.9 Domestic portable biogas shall be manufactured such as the deformation due to environmental 
condition shall not be greater than 2 % of the original measurements.  
4.1.1 0 Tensile strength shall not be less than 12 N/mm 2 and the dig ester shall not have any leakage while 
tested for hydrostatic pressure head test  
4.1.1 1 Domestic portable biogas shall be protected to prevent children and others from using it for purposes 
other than intended.  
4.1.1 2 Metallic material used for manufacturi ng of domestic portable digester shall be constructed in manner 
that enable the user to avoid hazards from them and shall be non corrosive materials.   
4.1.1 3 Material of construction of Biogas digester and Gasholder shall be such that it does not impart a ny 
colour, odour nor any toxic effect and it shall not contaminate biogas slurry.  
4.1.1 4 Digester shall be sized to retain the volume of manure and water at the design total solids 
concentration for the digester design retention time . 
4.1.1 5 Inlet and out let pipe shall be connected  to facilitate process flow and shall be made of 4” UPVC/PVC . 
Inlet connections shall be of 4’’ UPVC/PVC with adequate gaskets and check nut.  
4.1.1 6 Outlet connection shall be an integral  part of biogas digester  and shall be comp atible with 4’’ flexible 
UPVC/PVC pipe and joint finished in such a way that no leakage of biogas plant slurry takes  place d uring the 
life span of the domestic portable biogas plant . 
4.1.1 7 Gas outlet valve shall be of minimum ½’’ with inside threaded conn ections and leaving no chance of 
gas leakage at the base of joint with Gasholder  
4.1.1 8 Gas outlet connection shall be adequate for the gas outlet valve with adequate gasket and check  and 
gas outlet pipe shall be of PVC or HDPE 4.1.20  Internal and external  surface of the biogas digester and 
biogas holder shall be smooth, clean and free from other hidden internal defects, such as air bubbles, pits and 
metallic or other foreign material inclusions.  
4.1.19  Inlets shall be of any permanent type designed to re sist corrosion, plugging, freeze damage, and 
prevent gas loss.  
4.1.20 The digester shall be equipped with an outflow device, such as an underflow weir, that will maintain  
the operating level, maintain a gas seal under the cover, prevent gas loss, and relea se effluent directly to 
separation, storage, or other treatment facility.  
4.1.21 The biogas collection, transfer, and control system shall be designed to convey captured gas from 
within the digester to gas utilization equipment or devices (flare, boiler, e ngine, etc.).  
4.1.22 The gas collection system within the digester shall be designed to facilitate exclusion of floating 
debris.  
4.1.23 Pipe and components within the digester shall be securely anchored to prevent displacement from 
normal forces including loads from accumulated scum  
4.1.24 The digester cover shall be  designed for all internal and external loads  and shall capture and convey 
the biogas to  a designed gas outlet. The cover system  shall be designed to exclude the entrance  of air under 
all operat ing conditions.  
4.1.25 Pipes shall be constructed to enable all sections to be safely isolated and cleaned as part of routi ne 
maintenance.   
©RSB 2017 - All rights reserved                  6 
 4.1.26 Transfer pipe can be buried or installed above ground and must include provisions for drainage of 
condensate.  
4.1.27 Equipment and components shall have a service life of not less than 2 years and shall be readily 
accessible for replacement or repair.  The life span for the biogas digester shall not be less than 15 years.  
4.1.28 Gas pipe installed within buildings shall be of type approved for combustible gas.  
4.1.29 Where electrical service is required at  the control facility, the installation and all  electrical wire, 
fixtures, and equipment  shall meet the RS 116 -1 and National Electrical Code . 
4.1.3 0 Equipment nee ded to properly monitor the digester and gas production shall be installed as part of the 
system. The following equipment may be installed:  
a) Pressure gauge ; 
b) gas meter suitable for measuring biogas  
4.2 Biogas  production  
4.2.1  The biogas (biomethane) produced s hall be free from liquids particulate matter such dust, dirt and 
mist over the entire range of temperatures and pressures.  
4.2.2  The biogas shall be produced by anaerobic digestion of the biomass. The biomass shall containing 
substrates  for anaerobic diges tion such as : manure, sludge, household waste, agricultural waste, food 
residues.  
4.2.3  The feed material shall be mixed with water to make fluent slurry . Unwanted materials such as straw, 
stones and dirt shall be  removed before the mixing process.  
4.2.4  The biogas shall have the components that meet the requirements given in table 1 
Table 1  — Biogas composition  
S/N Components  Chemical formula  Range  
1.  Methane  CH 4 55 – 85 %  
2.  Carbon dioxide  CO 2 14 – 44 %  
3.  Nitrogen  N2 Trace  
4.  Hydrogen  H2 Trace  
5.  Hydrogen sulphide  H2S Trace  
6.  Vapour of water  H2O Trace  
5 Fittings  
The manufacture shall provide as much information to the consumer regarding fittings.  
6 Sizes  
6.1 The size of biogas digester shall be determined on the basis of the chosen retention time RT and the  
daily substra te input quantity Sd  
Vd = Sd × RT [m3 = m3/day × number of days/ ] DRS 349: 2017  
7                ©RSB 2017 - All rights reserved  
 Where Vd is in m 3 or L; 
Sd in m3/day or L/day;  
RT in Days;  
6.2 The minimum acceptable size of portable domestic biogas digester shall be not less than 0.5 m3 and 
the average minimum dai ly feedstock system can accept should be  10kg  
6.3 The retention  time must be sufficiently long to ensure that the amount of microorganisms removed with 
the effluent (digestate) is not higher than the amoun t of reproduced microorganisms . Digester retention tim e 
shall be not less than  20 days.  
7 Sampling  and criteria for conformity  
7.1 All the domestic portable biogas of same raw material, same type, size and produced under relatively 
uniform conditions of manufacture shall constitute a lot.  
7.2 The sample of port able domestic  biogas  shall be selected at random from the lot. In order to ensure 
randomness of selection, tables of random numbers shall be used.  
7.3 Sample size shall be in accordance with Table 1.  
7.4 Each selected biogas , as per Table 1, Column 2, sha ll be tested for the requirements in Table 2 below.  
Table 2 — Scale of sampling and criteria for conformity for domestic portable biogas  
S/N Lot size  Sample size  Acceptance number  
1.  Up to 50  1 0 Failure  
2.  200 2 0 Failure  
3.  300 3 0 Failure  
4.  500 5 0 Failur e 
5.  501 and above  8 1 Failure  
8 Marking  
8.1 All the Biogas plants produced shall be distinctly marked with the following information:  
a) manufacturer's name and address  or recognized trade mark ; 
b) net capacity, in  litres/cubic metre with daily quantity in Kg ; 
c) lot or batch number;  
d) country of origin;  
e) manufacturer date;  
f) material code ; and  
g) recyclable . 
8.2 The marking shall be carried out either by painting, moulding or by sticking the identification mark s on 
external surface of the biogas . The marking shall be permanent.   
©RSB 2017 - All rights reserved                  8 
 9 Installation  
9.1 Installation and commissioning of portable domestic biogas shall be done by the 
compan y/manufacturer’s authorized or competent personnel.  
9.2 The beneficiaries of biogas plants shall be provided “Operation and maintenance” manual in the 
printed form/ version along with  warranty and guarantee clauses . 
9.3 The supplier shall provide a brochure to the purchaser including information on installation 
instructions, cleaning procedures, safety precautions, disposal and proper caution and warning  signs . 
9.4 The brochure shall be in  at least two official languages used in Rwanda including Kinyarwanda  
10 Pre-requisites for setting up a  portable domestic biogas  
The following requirements shall be looked into before setting up a biogas plant:  
a) the indiv idual or the family shall have sufficient source of substrate ; 
b) sufficient space shall be available for  the biogas . This space shall preferably be near the source of 
substrate  and invariably be close to the place where gas shall  be used ; and  
c) sufficient quantity of water shall be available for mixing with fresh bio -mass before feeding . 
 DRS 349: 2017  
ICS 27.100 
 
 
©RSB 2017 - All right s reserved