THE PROJECT
The Agro chemical industry effluents is characterized by their high water usage during the manufacturing process. The effluent generated is comprised often of highly toxic and mainly polluted with the following:
- Biologically active biocides and inhibiting raw chemicals, active ingredients and by-products
- Solvents such as methanol, aromatic substances, di-chloro-methane, methyl-isobutyl-ketone(MIBK) from the formulations
- Higher Salinity
Typical effluents generated from s-Triazane, and substituted poly carbamates manufacturing facilities are polluted with:
- Up to 12,000 mg/lit COD comprising solvents in it
- Up to 600 mg/lit inhibitory, active ingredients and by products
- 500 to 800 mg/lit Total Kjeldahl Nitrogen (TKN) containing mostly Organic-N associated with slowly hydrolysable s-triazene.
- Up to 1500 mg/lit Sulfates (SO4-)
- 10,000 to 25,000 mg/lit Salt Concentration as NaCl
THE PROBLEM – Treatment of an agrochemical wastewater plant
Due to their adverse effects on the receiving environment, the treatment and removal of harmful substances present in the agrochemical effluents poses a serious challenge to both chemical treatment and biological treatment processes.
Because of the presence of a high amount of biologically degradable solvents, the conventional chemical wet oxidation processes is not cost effective and thus various biological processes especially conventional activated sludge systems are the most practiced treatment methods for agro chemical effluents.
However, high concentrations of inhibitory substances and salinity affect the biodegradation. The impact of the inhibitory substances and salinity is so severe that it reduces the removal efficiencies of a conventional activated sludge process in the range of 40-60%.
Additionally, due to the wide variations in the type of products manufactured and the basic raw materials used, the effluent generated fluctuates both qualitatively and quantitatively. Because of these variations, maintaining a stable aerobic biological process using activated sludge is quite challenging. Due to shock load events and the reduction in COD removal efficiencies, the sensitive nitrification process is either never properly established or inhibited severely. The presence of high amounts of salinity and inhibitory substances also play a crucial role in reducing nitrogen removal efficiencies for such effluents.
In addition to these inherent issues, high amounts of COD present in the effluent requires higher aeration energy for a fully aerobic treatment of agro chemical wastewater. Further to this, a fully aerobic process generates more toxic sludge which requires additional handling and treatment costs increasing the total cost of waste management for the industry.
THE SOLUTION – An Anaerobic-Aerobic MBBR/IFAS process
To increase the efficiency of the existing biological processes for the removal of persistent and hazardous pollutants, research conducted by various industries and academics during 80s indicated that:
- The persistence of pollutants is not exclusively related to structure, but rather also dependent upon environmental factors such as pH, temperature, bioavailability, the presence of additional substrate and development of required microorganisms, etc.
- Analogically to their synthesis, the biodegradation of organic molecules also occurs in several steps, catalyzed by enzymes produced through different microbial strains. That means that degradation of a pollutant is never a “product” of the activity of single strains, but rather a microbial consortium, comprised of several strains called mixed cultures.
- It has been observed that the treatment of persistent pollutants using two different metabolic pathways of anaerobic and aerobic treatment provides the most diversified consortium of micro organisms making the combined process more efficient than a single aerobic step.
Benefits of Anaerobic-Aerobic Process
- During the anaerobic process the complex structure of persistent pollutants undergoes a bioconversion and hydrolysis resulting in a lower molecular weight substance which is further easily mineralized aerobically in the subsequent aerobic step.
- A major fraction of the COD is removed during the anaerobic step which reduces the energy requirement of the aerobic process.
- The anaerobic process produces useful energy in the form of bio methane gas.
- The sludge production is lower when compared to an aerobic process resulting in lower handling and treatment cost of toxic solids.
Due to the complex chemical nature of the pollutants and adverse environmental conditions such as; high salinity, the presence of inhibitory substances, and pH, several types of microorganism such as nitrifying bacteria or pelletized anaerobic microorganisms do not tend to flocculate or become disintegrated and in some cases will often cause their wash out from the activated sludge resulting in process upsets and interruption.
In such cases, retaining specialized biomass as biofilms on highly porous, adsorbing, Levapor MBBR/IFAS media helps to overcome these problems.
The application of LEVAPOR MBBR/IFAS carriers for the Anaerobic-Aerobic treatment of Agro Chemicals effluent offer the following benefits:
- Immobilization of specialized biofilm colonies on highly adsorbent surface enabling better retention of active biomass in the reactor improving the biological process with a higher level of process stability.
- Provides higher resistance to fluctuations of pH, toxic and inhibitory substance concentrations, temperature, and salinity.
Pilot Testing
Based on the preliminary data available, a proposed anaerobic-aerobic configuration using the Levapor MBBR/IFAS media was tested in a lab scale plant which achieved 40-60% COD reduction under an aerobic only step while an anaerobic-aerobic combination provided 85-93% COD reduction.
After the initial lab scale confirmed the results, in order to determine the optimal, reliable process parameters under various qualitative and quantitative fluctuations of pollutant loads from the manufacturing process, a multiple step pilot plant was designed with the following process flow and was operated for a two year period.
Figure 1: Process diagram of pilot plant for biological treatment of effluent from pesticide production.
The long-term pilot testing under dynamic conditions indicated that the process was feasible and revealed maintaining a stable performance was possible as the results indicated below:
- the aerobic process – achieved approximately a 75 % COD removal, however the
- anaerobic-aerobic process – eliminated between 85 to 93 % of COD
It was concluded that the contribution of an anaerobic MBBR treatment was crucial to the whole process stability and reliability due to preliminary “cracking” of persistent and inhibitory compounds with enhanced hydrolysis of relatively stable triazine molecules to ammonia, which then further could be nitrified in the aerobic Levapor MBBR/IFAS process.
Biological removal of solvents, single chemicals and herbicides by an immobilized special biomass using LEVAPOR MBBR/IFAS media in the micro aerobic-anaerobic (MAE+ANA) and aerobic (AER) treatment step revealed the following results.
| Pollutant | Influent Concentrations | Overall Removal | Removal in different steps | |
| mg/L | % | 1. MAE + ANA | AER | |
| Aromatic Solvents | 1,5-3,0 | 100,0 | 90,0 | 10,0 |
| Methanol | 930-1980 | 100,0 | 95,0 – 100,0 | 0-5,0 |
| Dichloromethane | 4,0 – 4,2 | 100,0 | 100,0 | 0,0 |
| MIBK | 9,0 – 330 | 100,0 | 76,0 | 24,0 |
| Amines | 56 – 74 | 100,0 | 90,0 – 100,0 | 0,0 – 10,0 |
| Triazine derivatives | 96,5 – 114,3 | 100,0 | 64,2 | 35,8 |
| Carbamates | 17,8 – 24,3 | 80,0 | 72,0 | 28,0 |
| Herbicides total | 104 – 337 | 91,5 | 75 | 25 |
The influence of the process stability in the anaerobic step on biodegradation was more evident for the removal of herbicides. Under stable conditions, 92 % of triazine herbicides had been removed while under highly fluctuating conditions only 60% removal occurred which further caused upsets in the stable nitrification process.
Due to better hydrolysis of quite stable triazine structure rich in organic-N by anaerobic-aerobic treatment, a remarkably higher degree of overall nitrogen removal had been achieved in the denitrification-nitrification step compared to single aerobic only nitrification step.
THE RESULTS
Based on the long term pilot testing, a full scale plant based on the process presented in fig.1 to treat the effluent from an Agro Chemicals manufacturing facility was designed and commissioned.