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

WECC2015Engineering Innovation and Society

Kyoto, Japan29 November-2 December 2015

mmanyuchi@hit.ac.zw

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

Current situation

Sewage potential…….

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

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)

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

Sewage treatment with Acti-zymeParameter 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

SO42- (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

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

Models form

Where:K = ConstantX1 = TKN constantX2 = BOD5 constantX3 = TP constantX4 = COD constant

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

0 10 20 30 40 50 60 70 800.0

0.5

1.0

1.5

2.0

2.5

f(x) = − 0.000242360242229659 x² + 0.0244035065032914 x + 1.31883997754756R² = 0.964037437318699

f(x) = − 1.96366869863055E-05 x² + 0.00683648201918648 x + 1.25037092159308R² = 0.961221988616487

7 daysPolynomial (7 days)40 days

Acti-zyme loading (g/m3)

CO

D/B

OD

5

𝑪𝑶𝑫𝑩𝑶𝑫𝟓=𝟏 .𝟔𝟔𝟗+𝟎 .𝟎𝟎𝟖𝑻𝑲𝑵 −𝟎 .𝟎𝟎𝟖𝑩𝑶𝑫𝟓−𝟎 .𝟎𝟑𝟔𝑻𝑷 +𝟎 .𝟎𝟎𝟔𝑪𝑶𝑫

BOD5/TKN ratio

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

14

f(x) = 0.000647770773014539 x² − 0.0952037729531078 x + 7.86485945551112R² = 0.985683695098361

f(x) = − 0.00153534737714306 x² + 0.151149460567657 x + 6.68388404893894R² = 0.946487256301449

7 daysPoly-nomial (7 days)40 days

BO

D5/T

KN

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

𝑩𝑶𝑫𝟓𝑻𝑲𝑵 =𝟒 .𝟗𝟔𝟕−𝟐 .𝟒𝟓𝑻𝑲𝑵+𝟎 .𝟎𝟐𝟗𝑩𝑶𝑫𝟓+𝟎 .𝟏𝟒𝟖𝑻𝑷+𝟎 .𝟎𝟎𝟓𝑪𝑶𝑫

Biogas production potentialGas %

(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

Bio-solids production potentialParameter % Composition

Nitrogen 8.17±0.15Phosphorous 5.84±0.03Potassium 1.32±0.02Copper 0.0073±0.0002Iron 0.0087±0.0003Calcium 0.0079±0.002Magnesium 0.016±0.0021

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

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

Thank you