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Failure Analysis of a Dissolved Air Flotation Treatment Plant in a Dairy Industry

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Abstract

Environmental pollution in Nigeria presents an urgent need to assess wastewater treatment facilities in various industries. This article presents an assessment of dissolved air flotation (DAF) operation in a dairy industry. The industry was visited, wastewater treatment facilities were assessed (based only on efficacy to remove selected environmental health-related pollutants) and measurements of essential design and characterization parameters were taken. The study revealed that the averages of flow rate, biochemical oxygen demand at 5 days (BOD5), chemical oxygen demand (COD), suspended solids (SS) and total solids (TS) of the influent wastewater into the plant (DAF) were 3.45 L/s, 1652.37, 3304.67, 2333.82, and 4396.10 mg/L compared to effluent quality of 560.37, 1127.33, 172.33, and 1866.67 mg/L for BOD5, COD, SS, and TS, respectively. The pH of the wastewater is being adjusted by addition of lime before the effluent equalization tank and individual efficacies of the system were 66.09, 65.89, 65.89, 57.54, 8.68, and 94.49% for BOD5, COD, SS, TS, DS, and total nitrogen, respectively, with overall efficacy of 38.10%. It was concluded that failure (lower overall efficacy) of the system can be attributed to setting of lime in the oversized equalization tank (50 m3 instead of 16.82 m3 per 8 h shift), the lack of application of standardized engineering code and practices (provision of underground tank in the process, lack of complete coagulation processes, coagulation and flocculation units), lack of adequate aeration unit and lack of reliable systems for automatically adjusting dosage of coagulant and flocculant. Although, DAF unit is the centerpiece of a DAF-based system design, there are several other supporting systems important to optimal DAF operation. These observations, coupled with the analysis in this report, demonstrate that the facilities necessary to minimize continuous environmental pollution are lacking. Pollution will become an increasing problem unless pollution preventing codes and standards are developed; incorporated into government regulations and the regulations are enforced.

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Abbreviations

AMD:

Acid mining drainage

FEPA:

Federal Environmental Protection Agency

GLUMRBSSE:

Great Lake Upper Mississippi River Board of State Sanitary Engineers

MOP8:

Manual of Practice number 8

ρ:

Mass density of the fluid (kg/m3), ρl

θs :

Angle of the rack with horizontal (°)

βs :

Bar shape factor

μs :

Dynamic viscosity of the fluid (N s/m2)

Δt and t :

Time increment and time, respectively (d)

Δt eq :

Time interval over which samples were composite (h)

A sp :

Fine screen effective submerged open area (m2)

BOD5 :

Biochemical oxygen demand at 5 days (mg/L)

b s :

Minimum clear spacing of bars (m)

C 2eq :

Basin concentration after addition of flow for time Δt (mg/L)

C 2teq :

Basin concentration before addition of flow for time Δt (mg/L)

C ieq :

Basin average influent concentration over a period of Δt (mg/L)

COD:

Chemical oxygen demand (mg/L)

C si :

Fine screen coefficient of discharge (dimensionless)

D m :

Diameter of the impeller (m)

g :

Acceleration due to gravity (m/s2)

G :

Mean velocity gradient (m/s)

h Lc :

Head loss in a coarse screen (m)

h Lf :

Head loss in fine screens (m)

h v :

Velocity head of flow approaching the rack (m) \( = k_{\text{v}} (V_{\text{a}}^{2} /2g) \)

k mn :

Constant in mixing (varies with equipment used)

n r :

Number of revolution per second (r/s)

P l :

Power required in laminar condition (W)

P t :

Power required in turbulent condition (W)

P v :

Power required per unit volume (W/m3)

Q s :

Discharge through the fine screen (m3/d)

S eq :

Standard deviation of effluent wastewater concentration at a specified probability

S iq :

Standard deviation of influent wastewater concentration

t eq :

Equalization detention time (h)

w s :

Maximum cross-sectional width of the bars facing direction of flow (m)

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Author information

Authors and Affiliations

  1. Department of Civil Engineering, Federal University of Technology, Akure, Nigeria

    J. O. Babatola

  2. Department of Civil Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria

    K. T. Oladepo & I. A. Oke

  3. Department of Water Resources and Environmental Engineering, Ahmadu Bello University, Samaru-Zaria, Nigeria

    S. Lukman

  4. Department of Chemistry, Adeyemi College of Education, Ondo, Nigeria

    N. O. Olarinoye

  5. Obafemi Awolowo University, Ile-Ife, Nigeria

    N. O. Olarinoye

Authors
  1. J. O. Babatola
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  2. K. T. Oladepo
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  3. S. Lukman
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  4. N. O. Olarinoye
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  5. I. A. Oke
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Corresponding authors

Correspondence to J. O. Babatola or I. A. Oke.

Appendix: Derivation of Equations for Treatment Plant’s Efficacy

Appendix: Derivation of Equations for Treatment Plant’s Efficacy

The pollutants that are removed by the treatment plant can be divided into two parts of a and b; “a” represents the turbidity removed and “b” represents microorganisms reduced specifically bacteria. Under normal condition or operation of wastewater treatment pollutants are expected to be removed or reduce to FEPA [40] standard limits. Let F a denote the concentration of pollutant in the raw water (F), O a denote the fraction of “a” removed from the raw wastewater but in the floc (O), and U a denote the fraction of “a” present in the treated wastewater (U). Then the pollutant removed from the raw wastewater can be expressed as follows:

$$ F(F_{\text{a}} ) = O(O_{\text{a}} ) + U(U_{\text{a}} ) $$

which can be expressed as follows [28]:

$$ F = O + U $$

Elimination of O a or U a from the above equations

$$ \frac{F}{U} = {\frac{{O_{\text{a}} - U_{\text{a}} }}{{O_{\text{a}} - F_{\text{a}} }}} $$

and

$$ \frac{F}{O} = {\frac{{O_{\text{a}} - U_{\text{a}} }}{{F_{\text{a}} - U_{\text{a}} }}} $$

It can then be shown that the efficacies of the treatment plant in removing COD (E u) and BOD5 (E 0) are as shown:

$$ E_{\text{u}} = {\frac{{{\text{amount}}\;{\text{of}}\;{\text{COD}}\left( {\text{mg/L}} \right)\;{\text{removed}}}}{{{\text{total}}\;{\text{amount}}\;{\text{of}}\;{\text{COD}}\left( {\text{mg/L}} \right)\;{\text{of}}\;{\text{raw}}\;{\text{wastewater}}}}} $$
$$ E_{\text{u}} = {\frac{{O(O_{\text{a}} )}}{{F(F_{\text{a}} )}}} = {\frac{{O_{\text{a}} (F_{\text{a}} - U_{\text{a}} )}}{{(O_{\text{a}} - U_{\text{a}} )F_{\text{a}} }}} $$
$$ E_{0} = {\frac{{{\text{amount}}\;{\text{of}}\;{\text{BOD}}_{5} ( {\text{mg/L)}}\;{\text{removed}}}}{{{\text{total}}\;{\text{amount}}\;{\text{of}}\;{\text{BOD}}_{5} \left( {\text{mg/L}} \right)\;{\text{of}}\;{\text{raw}}\;{\text{wastewater}}}}} $$
$$ E_{0} = {\frac{{U - U(O_{\text{a}} )}}{{F - F(F_{\text{a}} )}}} = {\frac{{U(1 - O_{\text{a}} )}}{{(1 - F_{\text{a}} )F}}} = {\frac{{(O_{\text{a}} - F_{\text{a}} )(1 - O_{\text{a}} )}}{{(O_{\text{a}} - U_{\text{a}} )(1 - F_{\text{a}} )}}} $$

These indicate that overall efficiency of the treatment plant can be expressed as

$$ E = E_{0} E_{\text{u}} $$

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Babatola, J.O., Oladepo, K.T., Lukman, S. et al. Failure Analysis of a Dissolved Air Flotation Treatment Plant in a Dairy Industry. J Fail. Anal. and Preven. 11, 110–122 (2011). https://doi.org/10.1007/s11668-010-9430-z

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