Anaerobic digestion of cheese dairy wastewater following chemical oxidation

As global cheese production has gradually increased there has been a proportional increase in the wastewater produced which poses serious environmental problems. Conventional anaerobic treatment processes are often used for dairy wastewaters. However, lipids inhibition and high suspended solids concentrations are the main operational problems for anaerobic digesters treating dairy wastewater. The performance of a pilot scale cheese production wastewater treatment plant that includes an oxidation pretreatment stage and a UASB (upflow anaerobic sludge blanket) reactor was investigated. Monitoring was performed during the start-up period, the fully operational period and the period following wastewater depletion. The data from this six month period are presented and evaluated. The mean composition of raw wastewater was: chemical oxygen demand (COD) 20,314 mg l−1, total organic carbon (TOC) 7920 mg l−1, total Kjeldahl nitrogen (TKN) 285 mg l−1, total phosphate (TP) 85 mg l−1, fats 1931 mg l−1 and pH 4. In the oxidation pretreatment stage fats presented a significant reduction that reached 80% and the sharp peaks of the all pollution parameters of the raw wastewater were adequately smoothed. The anaerobic digester performance was considered satisfactory, since the COD reduction >90%. A significant fraction of the input carbon was retained in the sludge bed as “absorbed” carbon and then hydrolysed slowly following first order kinetics with a hydrolysis rate constant of 0.0036 d−1. The pilot plant operation showed that the proposed technology could be sustainable not only in terms of the treatment of cheese-dairy wastewater but for their energy utilisation as well.