Against the desirable limit of less than 1000 Chemical Oxygen Demand (COD), what could be the best techno economical solution to effluent treatment having methanol up to 1% and contributing COD up to 100,000? Here’s a report on the discussion picked up on the social network.
Wastewater coming from Distillery Industry i.e. Spent Liquor normally reports 55,000 – 60,000mg/l BOD and 100,000 – 120,000mg/l COD, pH acidic side i.e. 4.5 to 5.0 and temperature around 600 Centigrade with High Total Suspended Solids (TSS) contents as well. The flow rate might be up to 2,000 m3/d.
Generally, anaerobic treatment rather than aerobic treatment should be opted for, says EfrenBasco, Singapore. “With 100,000 COD, greater quantity of biogas can be extracted under controlled conditions. It is just a matter of converting methanol to methanoic acid and later to methane, carbon dioxide and water through anaerobic reaction. This can be further converted through aeration for waste disposal or further purification for water recycling.”
Seconding Efren views, Richard Bleam, Director of Technical Services at Bioscience, Inc, Allentown, Pennsylvania, says that anaerobic biological treatment is probably the most economical but if methanol is one per cent and COD is 100,000mg/L, there are a lot of other constituents. “You will need a treatability study to determine if the wastewater is toxic and to determine the concentrations that must be controlled to operate stable process.”
Anaerobic BC system for 100,000ppm, requires two tanks of two days HRT each with no sludge handling. It also comprises two low energy agitators with low capex and low opex. If it is a continuous flow, methane can be recovered and can actually have positive cash flow in the form of carbon credits. It will help get rid of 99% of COD or more. Explains Eros Kaw, Chief Tech Support at Biocleaner Inc., San Francisco, “It may depend on the flow rate and how many years you expect the flow. You need to also have a hurdle rate. One can do a Net Present Value (NPV) analysis with high strength wastewater.”
Anaerobic digestion would probably be best for such high COD concentration provided the wastewater is biologically degradable and non-toxic, then low- or medium-rate. “Considering wastewater as non-toxic, anaerobic digestion followed by advanced oxidation is a wise step. It helps in utilizing the UV and strong oxidant compound to break down the COD into Biochemical Oxygen Demand (BOD) and Activated Sludge Process (ASP),” suggests Ziaul HasanRizvi , Director, Brisanzia Technologies, New Delhi.
If concentration of Methanol and waste flow are going to be more or less constant, one should go for anaerobic treatment followed by aerobic such as Upflow Anaerobic Sludge blanket (UASB) technology, suggests DrUpendra Patel, Professor at Charotar University of Science and Technology, Anand. “This can further be followed by activated sludge. It has to be that there are no inhibitory compounds. I have designed UASB-ASP systems for industrial waste (organic chemical waste and confectionary waste streams) and they are running very well (UASB giving ~80% COD removal).”
Explaining further anearobic digestion (AD) + aerobic activated sludge (AS) approach, Bruno Peeters, water wizard, Antwerp Area, Belgium, says, “Using enhanced UASB, we convert over 90% of the COD to methane (CH4) resulting in less than 10% of the COD to be removed in the AS system thereby saving a lot of energy for aeration.”
However, says Sergio Silva, Adventech – Advanced Enviromental Technologies, Porto Area, Portugal, it is firstly essential to determine the toxicity of the wastewater. “You can do that with luminescent bacterias or in a simple lab scale biological reactor. If the wastewater is non-toxic, you can implement the suggested two biological stages anaerobic/aerobic. However, many industrial wastewater especially from some chemicals industries, are toxic for biological treatments. In these cases I suggest an AOP (Advanced Oxidation Process) pre-stage.”
Anaerobic Reactor/Digester followed by Aerobic Treatment will easily give COD 1,000m/l. This will give quite a good quantity of biogas to be used as alternate energy, says Krishnan Ganesan, Independent Utility Project Consultant, Tirunelveli Area.
Distillation could also be an option, opines DrAtharQuereshi, Process/Project Engineer (Group Leader) Water and Waste water at Rentec Environment Protection Technology LLC, UAE. This will give you high purity methanol, which is saleable. However, your operating cost could be higher because distillation is very energy intensive process. Also, it will depend on what are the other constituents in water besides methanol.”