1) The document presents research on using Acti-zyme, a bio-catalyst, to remove bio-nutrients from sewage through anaerobic digestion. Mathematical models were developed to simulate sewage treatment. 2) Testing showed Acti-zyme improved removal of nutrients like TKN, BOD5, and TP from sewage, meeting environmental guidelines. It also increased biogas production over untreated sewage. 3) The models can predict bio-nutrient removal ratios based on parameters like TKN, BOD5, TP and COD. Optimum removal occurred at 50g/m3 Acti-zyme loading and 40 day retention time. Treating sewage with Acti-zyme also

1. MATHEMATICAL MODELLING FOR BIO-NUTRIENT REMOVAL IN
SEWAGE USING ACTI-ZYME
By
M. M. Manyuchi, D.I.O Ikhu-Omoregbe, O. O. Oyekola, W. Zvarevashe and Z. Makumbe
WECC2015
Engineering Innovation and Society
Kyoto, Japan
29 November-2 December 2015
mmanyuchi@hit.ac.zw

2. Introduction
• Large amounts of sewage are being
disposed off without proper treatment1
• This results in eutrophication
• Need to effectively treat sewage to prevent
environmental challenges and harness value
added products
• Development of mathematical for simulating
industrial sewage treatment essential

3. Current situation

4. Sewage potential…….

5. Acti-zyme
• A bio-catalyst that promotes
digestion of sewage to produce
biogas
• Exists in pellet form
• Has been successfully used in
sewage treatment
• Allows for the removal of bio-
nutrients in wastewater
• Has been used in raw water and
piggery wastewater treatment
Acti-zyme pellets

6. Bio-nutrient removal in sewage
• Bio-nutrient removal in sewage is measured
through the biodegradability ratio
• These include:
– chemical oxygen demand to the biochemical
demand ratio (COD/BOD5),
– the BOD to the total Kjeldahl nitrogen ratio
(BOD5/TKN),
– the COD/TKN ratio and the COD to the total
phosphates ratio (COD/TP)

7. Sewage treatment methodology
• Retention time varied up to 60 days
• Acti-zyme loading: 35-70 g/m3
• Temperature: 35 oC
• Conditions: Anaerobic in 250 mL digesters
• Agitation: 60 rpm
• Sewage physicochemical parameters measured by
standard methods

8. Sewage treatment with Acti-zyme
Parameter Raw sewage Treated sewage EMA Guidelines
TKN (mg/L) 245±5.5 9.4±0.36 10-20
BOD5 @20 °C (mg/L) 557±15.3 41.8±1.08 30-50
TSS (mg/L) 608±16.1 37.3±1.02 25-50
TDS (mg/L) 535±13.2 59.4±0.53 500-1500
EC @25 °C (µS/cm) 3887±32.1 1070.4±0.36 1000-2000
CI- (mg/L) 833±11.2 263.3±4.02 -
pH @25°C 9±0.3 6.3±0.1 6.0-9.0
Coliforms (cfu/mL) 1x1011 1x108 ≤1000
TP (mg/L) 52±3.0 1.4±0.24 0.5-1.5
SO4
2- (mg/L) 1192±70.8 53.6±2.71 -
DO (mg/L) 7±0.2 87.0±0.20 ≥ 60
Temperature (°C) 22±1.5 37±0.5 < 35
COD (mg/L) 738±12.6 77.9±2.24 60-90

9. Modelling assumptions
• Linearity and additivity
• Statistical independence of variables
• Homoscedasticity i.e. constant variance of
the errors
• Normality of the error distributions
Modelling done at 95% confidence interval

10. Models form
𝑩𝒊𝒐𝒏𝒖𝒕𝒓𝒊𝒆𝒏𝒕 𝒓𝒆𝒎𝒐𝒗𝒂𝒍 𝒓𝒂𝒕𝒊𝒐
= 𝑲 + 𝑿 𝟏 𝑻𝑲𝑵 + 𝑿 𝟐 𝑩𝑶𝑫 𝟓 + 𝑿 𝟑 𝑻𝑷 + 𝑿 𝟒 𝑪𝑶𝑫
Where:
K = Constant
X1 = TKN constant
X2 = BOD5 constant
X3 = TP constant
X4 = COD constant

11. COD/BOD5 ratio
• COD/BOD5 ratios
greater than 1.2
indicating high rate of
biodegradation
• Biodegradation
increases with increase
in the ratio
• Biodegradation of
organic pollutants high
at 40 days
y = -2E-05x2 + 0.0068x + 1.2504
R² = 0.9612
y = -0.0002x2 + 0.0244x + 1.3188
R² = 0.964
0.0
0.5
1.0
1.5
2.0
2.5
0 20 40 60 80
7 days
40 days
Acti-zyme loading (g/m3)
COD/BOD5
𝑪𝑶𝑫
𝑩𝑶𝑫 𝟓
= 𝟏. 𝟔𝟔𝟗 + 𝟎. 𝟎𝟎𝟖𝑻𝑲𝑵 − 𝟎. 𝟎𝟎𝟖𝑩𝑶𝑫 𝟓 − 𝟎. 𝟎𝟑𝟔𝑻𝑷 + 𝟎. 𝟎𝟎𝟔𝑪𝑶𝑫

12. BOD5/TKN ratio
y = -0.0015x2 + 0.1511x + 6.6839
R² = 0.9465
y = 0.0006x2 - 0.0952x + 7.8649
R² = 0.9857
0
2
4
6
8
10
12
14
0 20 40 60 80
7 days
40 daysBOD5/TKN
Acti-zyme loading (g/m3)
• BOD5/TKN ratio was >4
for all the Acti-zyme
loadings
• BOD5/TKN values were
greater than 3 which was
an indication of low
biological de-nitrification
in the sewage especially
at 40 days retention time
𝑩𝑶𝑫 𝟓
𝑻𝑲𝑵
= 𝟒. 𝟗𝟔𝟕 − 𝟐. 𝟒𝟓𝑻𝑲𝑵 + 𝟎. 𝟎𝟐𝟗𝑩𝑶𝑫 𝟓 + 𝟎. 𝟏𝟒𝟖𝑻𝑷 + 𝟎. 𝟎𝟎𝟓𝑪𝑶𝑫

13. Biogas production potential
Gas %
(Acti-zyme)
%
(without Acti-
zyme)
CH4 72-78 53-65
CO2 16-20 22-27
Traces (H2S,
N2, H2)
5-9 8-12
Acti-zyme favours a clean bio-methane production with minimum trace gases

14. Bio-solids production potential
Parameter % Composition
Nitrogen 8.17±0.15
Phosphorous 5.84±0.03
Potassium 1.32±0.02
Copper 0.0073±0.0002
Iron 0.0087±0.0003
Calcium 0.0079±0.002
Magnesium 0.016±0.0021

15. Financial benefit
Product (per day) Cost ($)
Outputs Biogas 19 154.39
Bio-solids 43.01
Total 19 369.39
Less: Inputs Acti-zyme 5.125
Net Benefit 19 364.26

16. Conclusions
• Acti-zyme addition during anaerobic treatment of
sewage promotes bio-nutrient removal
• Optimum bio-nutrient removal was achieved at 50
g/m3 and 40 days retention times
• Mathematical models developed simulate industrial
sewage treatment
• Using Acti-zyme in sewage treatment has financial
and environmental benefits

18. Thank you