The Agro chemical industry effluents are characterized by their high water usage during the manufacturing process. The effluent generated from the manufacturing units is often highly toxic and mainly polluted with:
- Biologically active biocides and often inhibiting raw chemicals, active ingredients and by products
- Solvents like methanol, aromatic substances, di-chloro-methane, methyl-isobutyl-ketone(MIBK) from the formulations
- Higher Salinity
Typical effluents generated from s-Triazine, 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 Kjehldahl Nitrogen (TKN) containing mostly Organic-N associated with slowly hydrolysable s-triazine.
- 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 high amount of biologically degradable solvents, the conventional chemical wet oxidation processes are not cost effective and thus various biological processes especially conventional activated sludge system is the most practiced treatment method for the 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% only.
Additionally due to wide variations in the type of products manufactured and basic raw materials used, the effluent generated fluctuates both qualitatively and quantitatively. Because of these variations, maintaining stable aerobic biological process using activated sludge is quite challenging. Due shock load events and reduction in COD removal efficiencies, the sensitive nitrification process is either never established or inhibited severely. The presence of high amount of salinity and inhibitory substances also play crucial role in reducing nitrogen removal efficiencies for such effluents.
Besides these inherent issues, high amount of COD present requires higher Aeration energy for a fully aerobic treatment of agro chemicals wastewater. Further to this, fully aerobic process generate 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 existing bio processes for the removal of persistent and hazardous pollutants, the research conducted by various industries and academics during 80s indicated that:
- The persistence of pollutants is not exclusively related to structure, however 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 due to different microbial strains. That means that degradation of a pollutant is never a “product” of the activity of single strains, but of microbial consortia, comprising of several strains called mixed cultures.
- It has been observed that treatment of persistent pollutants using two different metabolic pathways of Anaerobic and Aerobic treatment provides the most diversified consortia of micro organisms making the combined process more efficient than single aerobic step.
Benefits of Anaerobic-Aerobic Process
- During the Anaerobic step the complex structure of persistent pollutant undergoes bioconversion and hydrolysis to lower molecular weight substances which are further mineralized aerobically quite easily in the subsequent aerobic step.
- A major fraction of the COD is removed during the Anaerobic step which reduces the energy consumption of the aerobic process.
- Anaerobic process produces useful energy in the form of bio methane gas.
- The sludge production is also lower compared to Aerobic process resulting in lower handling and treatment cost of toxic solids.
However, due to complex chemical nature of the pollutants and adverse environmental conditions like high salinity, presence of inhibitory substances and pH, several types of microorganism like nitrifying bacteria or pelletized anaerobic microorganisms do not tend to flocculate or become disintegrated in some cases which 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 the above problems.
Application of LEVAPOR MBBR/IFAS carriers for the Anaerobic-Aerobic treatment of Agro Chemicals effluent offer 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 higher level of process stability.
- Provides higher resistance to fluctuations of pH, toxic and inhibitory substance concentrations, temperature, and salinity.
Based on the preliminary data available, a proposed Anaerobic-Aerobic configuration using Levapor MBBR/IFAS media was tested in a lab scale plant which achieved 40-60% COD reduction under aerobic only step while Ana-Aer combination provided 85-93% COD reduction for lab scale plant.
After initial lab scale confirmation of the results, in order to determine optimal, reliable process parameters under various qualitative and quantitative fluctuations of pollutant loads due to contract manufacturing process, a multiple step pilot plant was designed with the following process flow and was operated for two years period.
The long-term pilot testing under dynamic conditions indicated that the process was feasible and maintaining stable performance was possible as 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 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 quite 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 immobilized special biomass using LEVAPOR MBBR/IFAS media in the microaerobic-anaerobic (MAE+ANA) and aerobic (AER) treatment step
|Pollutant||Inluent Concentrations||Overall Removal||Removal in different steps|
|mg/L||%||MAE + ANA||AER|
|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 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.
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.
The implementation of Micro Aerobic-Anaerobic-PreDenitrification-Nitrification treatment steps based on LEVAPOR MBBR/IFAS process for the Agro Chemicals effluent offered following benefits:
- Complete removal of Solvents, amines, MIBK, Triazines from the effluent.
- Stable Anaerobic and Nitrification processes achieving 85-93 % COD reduction.
- Remarkable nitrogen removal achieving lowest level of ammonical nitrogen and nitrates in the effluent eliminating TKN concentrations in the range of 300-800 mg/lit.
- Lower energy consumption and sludge production.