Reference number  
DRS  363: 2017  
© RBS yyyy 
© RSB 2017  
 
 RWANDA 
STANDARD  DRS  
363 
 
First edition  
2017 -mm-dd 
 
Tannery effluent — Safety disposal —
Requirements  
 
  DRS  363: 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 ascertain 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 utilized 
in any form or by any means, electronic or mechanical, including photocopying and microfilm, without 
prior written permission from R SB. 
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Rwanda Standards  Board  
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Tel. +250 252 586103/ 582945  
Toll Free: 3250  
E-mail: info@rsb.gov.rw  
Website: www.rsb.gov.rw  DRS  363: 2017  
iii                 ©RSB 2017  All rights reserved  
 
 Contents  Page 
1 Scope  ................................ ................................ ................................ ................................ ......................  1 
2 Normative references  ................................ ................................ ................................ ............................  1 
3 Term s and definitions  ................................ ................................ ................................ ...........................  1 
4 Requirements  ................................ ................................ ................................ ................................ .........  2 
5 Treatment  ................................ ................................ ................................ ................................ ...............  4 
Annex  A (normative)  Requirements of industrial wastewater discharged into environ ment  ...................  7 
 DRS  363: 2017  
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 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 th e WTO/TBT 
agreement on the prep aration, 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 363 was prepared by Technical Committee RSB/TC 013, Environment, Health and Safety . 
  DRS  363: 2017  
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 Committee membership  
The following organizations were represented on the Technical Committee on Environment, Health and Safety 
(RSB/TC 013) in the preparation of this standard.  
Golf Fish Limited  
Integrated Polytechnic Regional Centre – Kigali (IPRC -Kigali)  
Kigali Leather Ltd  
Ruliba Clays Ltd  
Rwanda utility regulation Agency (RURA)  
Star Construction & Consultancy (SCC)  
University of Rwanda – College of Science and Technology (UR -CST)  
Water & Sanitation Corporation (WASAC)  
Rwanda  Standards Board  (RSB) – Secretariat  
  DRS  363: 2017  
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 Introductio n 
Everyday a huge quantity of solid waste, including trimmings of finished leather, shaving dusts, hair, fleshing, 
trimming of raw hides and skins, are being produced from the industries. Chromium, sulphur, oils and noxious 
gas (methane, ammonia, and hydro gen sulphide) are the elements of liquid, gas and solid waste of tannery 
industries.  
Wastewaters from tanneries units are extremely complex mixtures containing considerable amounts of 
hazardous compounds, heavy metals such as Chromium, inorganic and organi c compounds that make the 
tanning industry potentially a pollution -intensive sector.  
Tanneries are one of the most prominent sources of chromium pollution to the aquatic environment (At high 
concentrations chromium is toxic, mutagenic, carcinogenic and ter atogenic).  If not adequately treated, 
wastewater from tanneries contaminates surface water and sediments to an unacceptable level. The solid 
waste from tanneries causes a major environmental problem through contamination of the soil, and 
groundwater apart from emission of huge quantities of greenhouse  gases to the atmosphere.  
Raw t annery effluent composition  
During the tanning process at least 300 kg of chemicals (lime, salt etc.) are added per ton of hides. Excess of 
non-used salts will appear in the wastewater. Because of the changing pH, these compounds can precipitate 
and contribute to the amount of solid waste or suspended solids  
Every tanning process step, with exception of the crust finishing operations, produces wastewater. An average 
of 35 m3 is produced per ton of raw hide. This wastewater contains:  
 salts (Cl), fat, protein, preservatives (soaking);  
 lime and ammonium salts, ammonia, protein (hair), and sulphides (fleshing, trimming, bating);  
 chromium(salts) and polyphenolic compounds (tanning); and  
 dye and solvent chemicals (wet -finishing).  
Tannery wastewaters often find their way into surface water, where toxins are carried downstream and 
contaminate water used for bathing, cooking, swimming, and irrigation. Chromium waste can also seep into 
the soil and contaminate groundwater systems that provide drinking water for nearby communities.  
 DRS  363: 2017  
1                 ©RSB 2017  All rights reserved  
 
 Tannery effluent  — Safety disposal — Requirements  
1 Scope  
This Draft Rwanda Standard provides minimum requirements f or treatment and safe disposal of tanner y 
effluent and its by -products.  
This document is applicable to tanneries only.  
It is not applicable to wastewater from domestic  and commercial buildings or oth er industries.  
2 Normative references  
The following referen ced documents are indispensable for the application 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.  
RS 109: 2017  Water quality  — Discharged industrial wastewater — Requirements  
RS 126-1: 2012 Waste water treatment plant — Part 1: Vocabulary  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions apply.  
3.1  
storm water  
water from rainfall or other natural  precipitation or from the melting of snow or ice  
3.2 
treated  effluent  
treated wastewater or effluent from the last stage of a wastewater treatment plant  
3.3 
tannery effluent  
tannery wastewater includes contaminated stor m water, cooling water, process waters and wash -down waters   
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 3.4 
biomethanation  
process by which organic material is microbiologically converted under anaerobic conditions to biogas  
3.5 
safety  
freedom from unacceptable risk  
3.6 
ultimate sludge  
sludge that can no longer be treated or transformed to reduce or eliminate completely its toxicity  
3.7  
waste water treatment system  
installed system from collection up to the disposal or discharge of produced wastewater  
4 Requirement s 
4.1 General requirements  
4.1.1  To prot ect the environment , in particular, water quality, tanneries shall be on suitable sites and shall 
have an appropriate wastewater treatment system that is correctly installed and maintained.  
4.1.2  Tannery effluent shall be collected, treated and disposed in  a manner that does not degrade the 
environment in order to prevent, eliminate or reduce their adverse effects on human health, natu ral resources, 
flora and fauna.  
4.1.3  Tanneries shall ensure that untreated wastewater does not discharge to watercourses through use of 
designated  wastewater treatment facilities and monitoring of wastewater discharges.  
4.2 Collection and draining systems  
4.2.1  Collection  
4.2.1.1  All wastewater produced within tannery premises and tanning process shall be immediately 
conveyed and cha nnelled to the treatment plant.  
4.2.1.2  Tannery effluent collection pipework shall drain directly to the treatment system to avoid any 
stagnation.  DRS  363: 2017  
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 4.2.2  Drainage system  
4.2.2.1  General  
4.2.2.1.1  A building shall have a drainage system for : 
a) adequate disposal of wastewate r from tanning process  for hygiene; and  
b) adequate disposal of surface water (rain water and/or storm water) from the building.  
4.2.2.1.2  No part of a drainage system conveying wastewater from tanning process shall be connected to a 
sewer reserved for surfac e water (rain water and/or storm water) and no part of a drainage system conveying 
surface water shall be connected to a sewer reserved for tannery effluent.  
4.2.2.1.3  Where authorized by the competent authority, the connection between sewer reserved for t annery 
effluent and municipal sewer system shall be accepted after tannery effluents have undergone pre -treatment 
and meet the quality of raw water discharged to municipal sewer system.  
4.2.3  Design of drainage system  
4.2.3.1  Tannery effluent drainage system shall be design ed in such  a way that it : 
a) convey all produced wastewater to a wastewater outfall, (sewer  system or a wastewater treatment 
system);  
b) minimise the risk of blockage or leakage;  
c) prevent foul air from the drainage system from entering the building  under working conditions;  
d) is ventilated to prevent the build -up of gases;  
e) is accessible for clearing blockages; and  
f) is adequately protected from accidental damage from sources such as traffic, ground settlement and tree 
roots.  
4.2.3.2  The capacity of the tannery effluent drainage system shall be large enough to carry the expected 
flow at any point in the system.  
4.2.3.3  Section of pipe that transport effluent to the treatment plant shall be able to support peak flow 
pressure and resistant to corrosion and oxidation.   
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 5 Treatment  
5.1 Treatment system  
5.1.1  A tannery effluent treatment  system shall be so designed, sited and constructed that:  
a) it is not prejudic ial to the health of any person;  
b) it does not cause a risk to p ublic health or the environment;  
c) it prevents unauthorised access but allows adequate means of acce ss for emptying and maintenance;  
d) it will function to a sufficient standard for the protection of health i n the event of a system failure;  
e) it has adequate capacity;  
f) it is impermeable to liquids; and 
g) it is adequately ventilated.  
5.1.2  Information on the wastewater treatment system and any continuing maintenance required to avoid 
risk to health and the environment shall be provided to the owner  and made available for all treatment system 
operat ing personnel . 
5.2 Treatment stages  
Tannery effluent shall undergo at least the minimum effluent treatment before its final disposal as described in 
clause 5.2.1 and 5.2.2 . 
5.2.1  Grease and g rit removal  
5.2.1.1  Hairs, shaving dusts, fleshing, trimming of raw hides and skins, trim mings of finished leather, and 
other solid wastes carried by the effluent stream shall be removed  and treated accordingly before disposal.  
5.2.1.2  Oil, fat and grease shall be separated from the effluent stream and managed accordingly.  
5.2.1.3  In the case there is a common effluent treatment plant, the tannery shall properly carry out the 
above stage (clause 5.2.1) and chromium pretreatment before wastewater reaches the general sewer system.  
5.2.2  Effluent treatment  
5.2.2.1 Produced tannery wastewater  shall be treated using appropriate technology and make sure the 
treated effluent  meets  the requirements of discharged industrial wastewater as stipulated in RS 109 :2017 . DRS  363: 2017  
5                 ©RSB 2017  All rights reserved  
 
 5.2.2.2 During  treatment, attention sh all be drawn to the removal of Chromium  and sul phur ions. Where 
possible , priority sh all be given to the reuse of chromium.  
5.2.2.3 Measures  shall be taken to avoid accident from sulphur gases.  
5.3 Treated effluent quality  and disposal  
5.3.1  The treated effluent  quality shall respect the quality requirement s provided in RS 109 :2017  (see 
annex A)  
5.3.2  The disposal of treated tannery effluents shall be subjected to an authorization issued by a recognized 
authority responsible for the protection of the environment.  
5.3.3  The reuse of tannery effluents shall respect the standards o n water quality imposed for its intended 
use 
5.3.4  The quarterly  monitoring documents and other performance documents of the tannery effluent 
treatment system shall be kept and available at the time of inspection . 
5.4 Sludge 
5.4.1  Sludge treatment  
5.4.1.1  Sludge from tannery effluent treatment shall  undergo further treatment  to reduce, mitigate and /or 
eliminate its toxic character . The chromium content shall not exceed 5000mg/kg.  
5.4.1.2  Sludge from tannery effluent treatment contains various hazardous chemicals in high 
concentration likely to cause various environmental impacts.  This complexity calls the combination of various 
methods and techni ques  for its management. Sludge treatment may include the following:  
h) reduction of v olume ( e.g. Using polyelectrolytes , and anaerobic digestion) ; 
i) dewatering,  (which may include the drying and compaction) ; 
j) converting sludge into by -products (e.g. Biomethanation and electricity generation) ; 
k) composting ; 
l) solidification and immobilisation of h eavy metals ; and  
m) incineration . 
5.4.1.3  When making choices in sludge management the hygienic aspects sh all be considered alongside 
the environmental impacts of the treatment such as energy use or emissions and the benefits of the final 
product.   
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 5.4.2  Sludge disposal  
5.4.2.1  The main parameters to be considered for sludge landfilling are:  
a) sludge rheology (important for the transport and incorporation to the other wastes);  
b) odours;  and 
c) dry matter content (important for the water balance of the landfill).  
5.4.2.2  The ultimate sludge shall be disposed into the sanitary landfill dedicated for tannery sludges . 
5.4.2.3  The ultimate tannery sludge discharge sh all be subject ed to an authorization issued by the 
national environmental protection authority, taking into acc ount the availability of safe and appropriate landfills 
for tannery sludge.  
5.4.2.4  The use of final sludge (e.g. as compost) shall respect the quality standards for its intended use 
after proof that it is safe for environment.  
 
Fig. 1  Layout of sanitary landfi ll dedicated for tannery sludge  
DRS  363: 2017  
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 Annex  A 
(normative)  
 
Requirements of industrial wastewater discharged into environment  
A.1 Chemical requirements  
Chemical requirements for industrial wastewater shall comply with the requirements given in Table A1 below.  
Table A1 — Chemical requirements for discharged industrial wastewater  
S/N  Parameter  Permissible limits 
(max.)  Test methods  
1.  pH 5-9 RS ISO 10523  
2.  Total suspended solids mg/l  50 RSISO 11923  
3.  Total Dissolved Solids mg/l  2000  RS ISO 7888  
4.  Oil and grease mg/l  10 ISO 9377  
5.  BOD5  mg/l (20°C)  50 RS ISO 5815  
6.  COD mg/l  250 RS ISO 6060  
7.  Ammonia (as N) mg/l  20 RS ISO 6778  
8.  Phosphates mg/L  10 Analytical tests (capillary 
electrophoresis)  
9.  Free chlorine mg/L  1.0 ASTM D1253 -14 
10.  Arsenic mg/l  0.01 ISO 11969  
11.  Benzine mg/l 0.1 ISO 11423  
12.  Cadmium mg/l  0.1 ISO 5961  
13.  Hexavalent Chromium mg/l  0.05 ISO 23913  
14.  Copper  mg/l  3 ISO 8288  
15.  Cyanide mg/l  0.1 ISO 6703  
16.  Iron mg/l  3.5 RS ISO 6332  
17.  Lead mg/l  0.1 ISO 8288  
18.  Mercury mg/l  0.002  ISO 5666  
19.  Nickel mg/l  3 ISO 8288  
20.  Phenol mg/l  0.2 ISO 8165  
21.  Sulphide mg/l  1.0 ISO 13358  
22.  Zinc mg/l  5 ISO 8288  
23.  Selenium mg/L  0.02 ASTM D3859 -15 
24.  Pesticides mg/L  Not detectable  ASTM D8025 -16  
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 A.2 Physical requirements  
Physical requirements for industrial wastewater shall comply with the requirements given in Table A2 below.  
Table A2 — Physical requirements for discharged industrial wastewater  
S/N Parameter  Requirements  Test methods  
1.  Temperature increase °C  < 3  Thermometer[1]  
Note [1]The thermometer used should be calibrated according to National Measurement Law  
A.3 Microbiological requirements  
Microbiological requirements for industrial wastewater shall comply with the requirements given in Table A3 
below.  
Table A3 — Microbiological requirements for discharged industrial wastewater  
S/N Parameter  Permissible limits  Test methods  
1.  Faecal Coliforms cfu /100ml  400 RS ISO 4831  
.  DRS  363: 2017  
9                 ©RSB 2017  All rights reserved  
 
 Bibliography  
[1] RURA regulations , Directives on minimum requirements for liquid wastes  disposal and treatment, of 
11/11/2009  
[2] RS ISO 24511:2007  Activities relating to drinking water and wastewater services — Guidelines for the 
management of wastewater and for the assessment of wastewater  
 DRS  363: 2017  
ICS 13.060.30  
 
 
©RSB 2017 All  rights reserved