OPTIMIZATION OF THE EFFLUENT TREATMENT 
SYSTEM (ANAEROBIC/AEROBIC) FOR RUBBER 
INDUSTRY BY KINETIC MODELING 
- • j C.J l!'.. 
• - • . • 
Indika Upuli Hettiarachchi 
This thesis was submitted to the Department of Chemical <& Process 
Engineering of the University of Moratuwa in partial fulfillment of the 
requirements for the Degree of JVf.Sc. in Polymer Technology 
(2000/2001).
 r v c . - c 
Department of Chemical & Process Engineering 
University of Moratuwa 
Sri Lanka. x ^ 
December, 2003. 
Univers i tv of M o r a t u w a . ~7 ^ / G &h ^ 
7 9 6 2 9 
Page iBBiEtsir 
I 
AJbsitracit II, in, IV 
Lis t of tobies, f igures, anmeswres VI,VH,VIIIJX 
Lis t of synmboBs & fflcromyomis X, X I 
Chapiter 1: Imtrod aactSoim 
1.1 The natural rubber industry in Sri Lanka 1 
1.2 Environmental problems caused by the natural rubber industry in Sri Lanka 2 
1.3 Environmental pollution control in rubber processing industry 3 
1.4 Scope of the study 4 
LS Objectives 5 
Chapter 2: Lterator® Review 
2.1 Rubber effluent characteristics 6 
2.1.1 Concentrated latex production process 7 
2.1.1.1 Production process 7 
2.1.1.2 In-plant pollution control 11 
2.1.2 Processing of latex into crepe rubber 11 
2.1.2.1 Production processes 11 
2.1.2.2 In-plant pollution control 15 
2.2 Treatment of wastewater 1 g 
2.2.1 Classification of wastewater treatment methods V ,^- • -18"' 
2.2.1.1 Physical treatment methods 18 
2.2.1.2 Chemical treatment methods 18 
2.2.1.3 Biological treatment methods 19 
2.3 Biological treatment processes 19 
2A The RRI based cost effective biological treatment process 20 
2.4. I The mechanism of anaerobic digestion 24 
2.42 Biological processes in the aerobic tanks 26 
2.4.3 Factors depending on the growth of bacteria 27 
2.4.3J The pH 27 
2.4.3.2 The alkalinity 28 
2.4.3.3 The temperature 28 
2.4.3.4 Nutrients 28 
2.5 Biological treatment for industrial wastewater 29 
2.5. 1 Nutrient & growth factor requirements 30 
2.5.2 Kinetics of biological growth 30 
2.5.2.1 Cell growth 31 
2.5.2.1.1 Cell growth & substrate utilization 31 
2.5.2.1.2 Effects of endogenous metabolism 31 
2.5.2.1.3 Effects of temperature 32 
2.6 Activated-sludge process 34 
2. 6. 1 Process design 3 5 
2.6.2 Process description 3 5 
2.6.3 Process microbiology 36 
2.6.4 Process analysis 37 
2.6.5 Process design & control relationships 39 
2.6.5.1 Sludge production 40 
2.6.5.2 Oxygen requirements & transfer 40 
2.6.5.3 Nutrient requirements 41 
2.6.5.4 Effluent characteristics 41 
2.6.6 Process control 41 
2.6.6.1 Dissolved- oxygen control 42 
2.6.6.2 Return activated-sludge control 43 
2.6.6.3 Sludge wasting 44 
2.6.6.4 Oxygen-uptake rates 45 
Chapter 3: Materials & Methods 
3.1 The experimental apparatus 46 
3.1.1 Measurement of BOD using BOD apparatus 47 
3.1.2 The VSS test 48 
3.2 Operating conditions of the full-scale activated-sludge process 48 
Chapter 4: Results & Discussion 50 
4.1 Calculation of important parameters (Y, ka, K 8, k, u^ ,) 
4.1.1 Determination of Y & kj 51 
4.1.2 Determination of Ks, k, jxm 52 
4.1.3 Full-scale plant data 57 
Chapter 5: Conclusions 65 
References 
I 
Declaration 
I hereby declare that this submission is a result of work carried out by me & to the 
best of my knowledge, it contains no material previously written or published by 
another person nor material which has been accepted for the award of any degree or 
acceptable qualification of a university, or other institute of higher learning except 
where the due reference to the material is made. 
Indika Upuli Hettiarachchi. 
December, 2003. 
n 
A b s t r a c t 
Raw rubber processing factories generate large amounts of wastewater containing 
organic pollutants & various process chemicals. Factory effluents exhibit high 
BOD (Biochsrnical Oxygen Demand) & COD (Chemical Oxygen Demand) 
concentrations, ammonia & suspended solids that are amenable to biological 
treatment methods. 
Rubber Research Institute (RRI) of Sri Lanka developed a novel &. cost effective 
biological effluent treatment technique for rubber-processing effluents discharged 
by creps robber & centrifuged latex factories. Treatment system, based on high 
rate anaerobic digestion coupled with aerobic stabilization also consists of settling 
& sand filtration. The main feature of this technique is the use of a low cost, septic 
tank type anaerobic digester filled up with coir fibres for the attachment of useful 
microorgsinisnis for effective biological conversion. Biological kinetic expressions 
have been derived for the design & control of effluent treatment plants where 
aerobic digestion is used commonly as the only treatment method. The kinetic 
coefficients in these expressions are widely used in design calculations. For a 
specified waste, a given biological community & a particular set of operating 
conditions the kinetic coefficients are fixed. Kinetic coefficients used for the 
design of domestic effluent treatment plants cannot be applied for the design of 
industrial effluent treatment plants as the waste composition & biological 
communities involved are different. Also kinetic coefficients for the anaerobically 
pretreated wastewater could be very different to those of the raw wastewater even 
for the same type of waste. No kinetic study has been carried out yet for the RRI 
developed treatment process for making possible improvements & modifications 
for optimal operation & performance of the aerobic treatment system to reduce 
capital, operational & maintenance costs under low loading conditions. 
The objective of this study is to find out the kinetic coefficients required for the 
design of activated sludge process from anaerobically pretreated rubber industry 
i n 
wastewater. The obtained values of kinetic coefficients were used to model an 
existing treatment system. 
A pilot-scale continuously aerated stirred tank was used as a model reactor. 
Reactor was operated without a recycle stream & fed with a steady flow of 
anaerobically pre treated wastewater obtained from a full-scale rubber industry 
effluent treatment plant. Samples were taken for five different runs at five 
different mean-cell residence times (6 t ) . BOD & MLVSS (Mixed Liquor Volatile 
Suspended Solids) of each sample for each run were measured according to 
Standard Methods for the Examination of Water & Wastewater. 
The following kinetic coefficients were estimated by a graphical method using 
measured data & the standard kinetic expressions. 
o Y = cell yield coefficient 
o kd = cell decay coefficient 
o Kg = half-velocity constant 
o k = maximum substrate concentration per unit mass of microorganisms 
o Um = maximum specific growth rate). 
The obtained kinetic coefficients show significant differences to those of domestic 
wastewater reported in literature. Maximum substrate concentration per unit mass 
of microorganisms (k) is less than one-half of the corresponding value for 
domestic wastewater. This implies more than double the concentration of 
microorganisms is required to be maintained in the aeration tank than that for 
domestic wastewater. Half-velocity constant (Kg) is more tham double the 
concentration of the corresponding value for domestic wastewater. It implies that 
the microorganisms have high affinity to anaerobically digested substrate. This 
could be expected because most anaerobically digested intermediate products & 
end products are considered good substrates for heterotrophic organisms. The cell 
yield coefficient (Y) is comparatively higher & the cell decay coefficient (kj) 
relatively lower than those for domestic wastewater leading to a higher Um, 
rv 
maximum specific growth rale. Therefore a richer microorganism concentration 
t 
could be expected in the aeration tank. 
Obtained kinetic coefficients were used to model an existing activated sludge 
treatment system. The minimum mean-cell residence time calculated with the 
obtained kinetic coefficients lead to a value of 0. 9(d) with a safety factor of 3.33 
& is within the accepted range for plant operation (2 - 20). Sludge washouts are 
very unlikely due to the fulfillment of the condition 0 c >l /u n i indicating a good 
waste stabilization. Calculations revealed significant difference between the 
predicted & operated condition of the plant. The obtained kinetic coefficients were 
used to optimize the plant operation by estimating sludge recirculation rate, 
aeration rate & sludge production rate. The findings will help improve the 
treatment system design & reduce the associated costs. 
Aclkim©wll©dlge]im®initi 
I wish to thank my supervisor Dr. S.L.J. Wijekoon for the guidance & advice given to 
me throughout in completing this research project. 
I am also grateful to 
o Dr. W. M. G. Seneviratae, Head, Chemical Engineering & Processing unit, 
Rubber Research Institute of Sri Lanka 
o Mr. K. Subramanium, M.Sc. course coordinator, Chemical & Process 
Engineering Department, University of Moratuwa 
o Dr. Shantha Walpolage, Mrs. Shantha Maduwage & all the other staff 
members of Chemical & Process Engineering Department, University of 
Moratuwa who helped in numerous ways in carrying out the project 
o The non-academic staff of Chemical & Process Engineering Department, 
University of Moratuwa especially Mr. H. R. Saraneris, Mr. Shantha Peiris & 
Mrs. Dinusha Martino who provided the assistance in the experimental work 
o Mr. Sarath Siriwardene & the staff of Chemical Engineering & Processing 
unit, Rubber Research Institute of Sri Lanka 
o Mr. Navindra Alponso, Instructor, Chemical & Process Engineering 
Department, University of Moratuwa 
o Mr.Lalith Gunatilake 
o Miss Dumila Panditha 
0 Mr. Prasanga Gunaratae, Mr. Pubudu Perera & Mr. Madura Ekanayake who 
were always ready to provide their assistance whenever required. 
1 will be indebted to Asian Development bank for granting financial assistance for 
the course of study. 
VI 
List of TatoEes page number 
T&blle 1: Total rubber production 1 
2: The average chemical composition of rubber processing effluents 6 
3: Characteristics of wastewaters from concentrated latex manufacture 9 
4: Average chemical composition of combined wastewaters & wasteloads 10 
T a b l l e 5: Standards stipulated by the Central Environmental Authority of 
Sri Lanka for the discharge of wastewater from concentrated latex 
production into inland waters 10 
T a b l e 6: Wastewater characteristics of crepe rubber manufacturing 15 
7: Standards stipulated by the Central Environmental Authority of 
Sri Lanka for the discharge of natural rubber industry wastewater 
into inland waters 16 
Table 8: Average performance & operating conditions of the ASP 4f 
9: Substrate & biornass concentrations for the five runs 59 
.0: Comparison of k i n e t i c coefficients for domestic, rubber & soap industry 
W a s t e w a t e r 57 
1 1 : Full-scale plant data 5 8 
TabDe 1 2 : Predicted operating conditions of the full-scale ASP using kinetic 
coefficients for domestic wastewater & from this study 64 
VII 
List of Figuares page mmimibsr 
Figure 1: Concentrated latex production process 8 
Figure 2: Processing latex into crepe rubber 12 
Figure 3: Processing latex into sole crepe rubber 13 
Figure 4: Processing field coagulated latex into scrap rubber 14 
Figure 5: Processing of latex into Ribbed Smoked Sheet Rubber 14 
Figure 6: Design of a RRI developed treatment plant 17 
Figure 7: The aerobic in nature 1% 
Figure 8: The anaerobic in nature 73 
Figure 9: Aerobic digestion mechanism 7'4 
Figure 10: Schematic diagram of the treatment plant adopted by the Rubber 7'4 
Research Institute of Sri Lanka (RRI) 
Figure 11: Schematic of a complete-mix reactor without recycle 33 
Figure 12: Schematic of complete-mix reactor with cellular recycle & wasting 37 
from the recycle line 
Figure 13: Typical mass balances for Return-sludge control ^ 
a) aeration tank mass balance b)secondary clarifier mass balance ^ 7£ 
Figure 14,14': Plot to determine kinetic coefficients Y & kj / K g & k 54/55 
VIII 
[DEES page number 
Annex 1: Consultancy services to rubber industry 67 
Annex 2: Reports on the rubber factory wastewater treatment & disposal 
Rubber production in Sri Lanka 69 
Annex 3: Technologies of wastewater treatment used in the Sri Lankan 
rubber industry 70 
Annex 4: Technologies of wastewater treatment used in the Sri Lankan 
rubber industry 71' 
Annex 5: Figure 7: The aerobic in nature 7% 
Annex 6: Figure 8: The anaerobic in nature 73 
Annex 7: Figure 9: Aerobic digestion mechanism 
Figure 10: Schematic diagram of the treatment plant adopted by 
the Rubber Research Institute of Sri Lanka 1%. 
(RRI) 
Annex 8: Figure 13: Typical suspended solids mass balances for 
Return-sludge control 
a)aeration tank mass balance 
b)secondary clarifier mass balance IB 
Annex 9: BOD & COD removal efficiencies & variation of pH after 
anaerobic treatment 76 
Annex 10: COD removal efficiencies of aerobic treatment 7TJ 
Annex 11: COD removal efficiencies after sedimentation & filtration 
Annex 12: Summary of the overall removal efficiencies of COD, BOD, 
TS,N&Pafter treatment 
X 
Lis t ofsynniilboOs & acinoimyinms 
d 
d" I-j 
dX/dt = rate of change of microorganism concentration in the reactor measured in 
terms of raassfVSS), mass VSS/(volume.time) 
Ko = half-velocity constant, mass/volume 
k = Ho/Y, niasimum rate of substrate utilization per unit mass of microorganisms, 
time'1 
kd = endogenous decay coefficient, time'1 
No= influent TKN, mass/volume 
N = effluent TKN, mass/volume 
P x = net weight of activated sludge produced each day, measured in terms of VSS, 
Ib/d (kg/d) 
Q = flow rate, volume/time 
Q ' w = cell wastage rate from recycle line, volume/time 
Q a= flow rate of effluent from the solids separation unit, volume/time 
ra = rate of bacterial growth, mass/volume.time 
= substrate utilization rate, mass/volume.time 
r'g = net rate of bacterial growth, mass/volume.time 
rx = reaction rate at T 
r2o= reaction rate at 20°C 
S = concentration of growth limiting substrate in solution or substrate concentration in 
effluent, mass/volume 
So - substrate concentration in influent, mass/volume 
So-S = mass concentration of substrate utilized, mass/volume 
E = process efficiency 
t = tonne 
T = temperature, °C 
U = specific substrate utilization rate, time 
V r = volume of the reactor 
V a = volume of the settling tank 
Vx = volume of reactor plus volume of settling tank 
Xo = concentration of microorganisms in the influent, mass VSS/volume 
X = concentration of microorganisms in the reactor, mass VSS/volume 
XI 
Xr = microorganism concentration in return sludge line, mass VSS/volume 
X e = microorganism concentration in effluent from me solids separation unit, 
mass VSS/volunie 
Y = maximum yield coefficient, mg/mg (ratio of the mass of cells formed to the mass 
of substrate consumed, measured during any finite period of logarithmic growth) 
Yobs - observed yield, 
0 = hydraulic retention time 
9 C = mean cell-residence time 
6,* = mean cell- residence time based on the total system 
1/0C = net specific growth rate 
'0' = temperature activity coefficient 
p. = specific growth rate, time"1 
u.
 m = maximum specific growth rate, time*1 
p,' = net specific growth rate, tame'1 
ASP = Activated Sludge Process 
BOD = Biochemical Oxygen Demand 
COD = Chemical Oxygen Demand 
DO = Dissolved Oxygen 
DRC = Dry Rubber Content 
XRRDB = International Rubber Research Development Board 
MLSS = Mixed Liquor Suspended Solids 
MLVSS = Mixed Liquor Volatile Suspended Solids 
OUR = Oxygen Uptake Rate 
RAS = Return Activated-Sludge 
RCCSR = Rubberized Coir Carrier Septic Tank Reactor 
RRI = Rubber Research Institute 
RRIM = Rubber Research Institute of Malaysia 
RSS = Ribbed Smoked Sheet 
SBR = Sequencing Batch Reactor 
SOUR = Specific Oxygen Uptake Rate 
TKN = Total Kjeldal Nitrogen 
TMFD = Tetra-Methyl-Thiuram-Disulphide 
TOC = Total Organic Carbon 
TSR = Technically Specified Rubber 
WAS = Waste Activated-Sludge