Post Treatment of Composting Leachate by Means of Ozonation and Granular Activated Carbon (GAC) Adsorption

There are different methods for treatment of composting leachate. Parameters dictating which
method to be chosen include quantity and quality of the leachate, required amount of
treatment and economical issues. Integration of ozonation and GAC adsorption into a single
process is one of the attractive methods for post treatment of wastewater. Therefore, post
treatment of composting leachate by means of ozonation and granular activated carbon (GAC)
adsorption was considered as the main objective of this study.
This study was conducted in laboratory scale and in batch mode. The set-up of batch system
consisted of a Plexiglas column with 20 mm inner diameter and 800 mm height. The tall
height of the column provides the required contact time between ozone and pollutants. Ozone
was supplied to the column through a diffuser sited at its bottom. The outlet gas of the reactor
may contain some residual ozone and can cause air pollution. Therefore, it is dangerous for
the people working nearby the reactor. Thus, the ozone in the gas phase leaving the column
was removed by KI solution. All experiments were conducted at room temperature (24 ±2°C).
The leachate used in this study was obtained from the effluent of the Leachate Treatment
Plant of Rasht Composting Facility (Guilan, Iran). All the chemicals employed for analysis
were analytical grade and obtained from the reliable companies.
In order to conduct the experiments, after complete determination of the specifications of
GAC as an adsorbent, different dosages of GAC were added to 800 mL of leachate with the
given initial concentration and pH in the column. The pH value of the solution was adjusted
by Sulfuric Acid or Sodium Hydroxide as needed. Then the ozone gas was introduced into the
column and the samples were taken in different intervals of time. After that required
parameters of the samples were measured. Ozone generator (ARDA-COG 5S) with 5 gr/hr
nominal capacity was used to produce ozone gas from pure and dry oxygen. Before starting
each step of the experiment, the ozone generator was calibrated for ozone concentration.
Pressure and flow rate of ozone gas produced was equal to 2 bara and 1 liter per minute,
respectively.
The results showed that integrated treatment of the leachate with ozonation and activated
carbon adsorption, namely catalytic ozonation, was more effective than each process solely.
In this study, COD removal rate of 44% in adsorption process, 57% in ozonation process and
80% in integrated process was achieved after 60 minutes. According to the results, in the
integrated process, addition of the adsorbent (as long as it floats in the leachate) has positiveeffect on the removal of organic load. The pH value is another important parameter that
affects the removal rate in the integrated process. It was found that removal of organic load is
more evident at basic condition than at acidic condition. In this study, the maximum COD
removal was achieved in the pH values between 8 and 9. Furthermore, in this process,
ozonation along with adsorption process resulted in reactivation of activated carbon and
avoided frequent GAC regeneration. After 5 times of the reuse of virgin GAC through a
consecutive experiment, only 7% loss in COD removal was observed in the integrated
process, while it reached to 95% for single adsorption process at the same condition. This can
be explained either by the predominance of catalytic reactions rather than adsorptionoxidation
reaction in the process or to the in situ regeneration of GAC.