Journal of Failure Analysis and Prevention

, Volume 11, Issue 2, pp 110–122 | Cite as

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

  • J. O. Babatola
  • K. T. Oladepo
  • S. Lukman
  • N. O. Olarinoye
  • I. A. Oke


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.


Environmental pollution Dissolved air flotation Health-related pollutants Efficacy Standardized engineering code 



Acid mining drainage


Federal Environmental Protection Agency


Great Lake Upper Mississippi River Board of State Sanitary Engineers


Manual of Practice number 8

List of Symbols


Mass density of the fluid (kg/m3), ρl


Angle of the rack with horizontal (°)


Bar shape factor


Dynamic viscosity of the fluid (N s/m2)

Δt and t

Time increment and time, respectively (d)


Time interval over which samples were composite (h)


Fine screen effective submerged open area (m2)


Biochemical oxygen demand at 5 days (mg/L)


Minimum clear spacing of bars (m)


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


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


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


Chemical oxygen demand (mg/L)


Fine screen coefficient of discharge (dimensionless)


Diameter of the impeller (m)


Acceleration due to gravity (m/s2)


Mean velocity gradient (m/s)


Head loss in a coarse screen (m)


Head loss in fine screens (m)


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


Constant in mixing (varies with equipment used)


Number of revolution per second (r/s)


Power required in laminar condition (W)


Power required in turbulent condition (W)


Power required per unit volume (W/m3)


Discharge through the fine screen (m3/d)


Standard deviation of effluent wastewater concentration at a specified probability


Standard deviation of influent wastewater concentration


Equalization detention time (h)


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


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Copyright information

© ASM International 2011

Authors and Affiliations

  1. 1.Department of Civil EngineeringFederal University of TechnologyAkureNigeria
  2. 2.Department of Civil EngineeringObafemi Awolowo UniversityIle-IfeNigeria
  3. 3.Department of Water Resources and Environmental EngineeringAhmadu Bello UniversitySamaru-ZariaNigeria
  4. 4.Department of ChemistryAdeyemi College of EducationOndoNigeria
  5. 5.Obafemi Awolowo UniversityIle-IfeNigeria

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