Dr. Bajnóczy Gábor Tonkó Csilla HIGH OXYGEN DEMANDING NON-TOXIC WASTEWATERS BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS DEPARTMENT OF CHEMICAL AND ENVIRONMENTAL PROCESS ENGINEERING FACULTY OF CHEMICAL AND BIOCHEMICAL ENGINEERING

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HIGH OXYGEN DEMANDING NON-TOXIC WASTEWATERS Contain significant amount of biodegradable organic matter, non-hazardous to aquatic life. Main sources: municipal wastewater livestock liquid manure food industry

EFFECT OF HIGH OXYGEN DEMANDING, NON-TOXIC WASTES ON NATURAL WATER high oxygen demanding wastewater flows Into natural water Dead organic matter in natural water (leaf, dead corpus, etc.) is decayed by bacteria using dissolved oxygen. The process is named mineralization and the final products carbon dioxide and water. Number of aquatic bacteria is limited by the available organic matter Increase of nutrients for the bacteria number of decomposing organisms increases significantly oxygen consumption increases ↓ dissolved oxygen in water decreases natural water: aerobic  anaerobic The process induced by non toxic organic materials in natural waters

PRODUCTS OF BIOLOGICAL DEGRADATION, AEROBIC AND ANAEROBIC CONDITIONS Independently of water condition – aerobic or anaerobic – life is always present, only the living forms and the final product of organic metabolism differ (aerobic or anaerobic bacteria). Aerobic conditionsAnaerobic conditions carbon nitrogen sulfur phosphorus carbon nitrogen sulfur phosphorus CO 2 NH 3 HNO 3 H 2 SO 4 H 3 PO 4 CH 4 NH 3 amines H 2 S PH 3 other phosphorus compounds Flame in marsh. phosphorus hydrogen + air  exothermic oxidation The heat evolved ignites the methane aerobic: oxygen is available ; anaerobic: lack of oxygen; anoxic: oxygen available only in form of eg.: nitrate, sulfate

BIOLOGICAL DEGRADATION OF ORGANIC COMPOUNDS 1. terminal oxidation of the carbon chain cytochrom-P450 (iron-containing enzyme) + oxygen in molecule R – CH 2 – CH 2 – CH 3 R – CH 2 – CH 2 – C - OHR – CH 2 – CH 2 – COOH Simplified mechanism of the terminal oxidation and the formation of carboxyl group at the end of chain 2. step: β – oxidation enzymes playing significant roles in the process: koenzyme – A : CoASH (reactive center: –SH thiol group) hydrogen transfer enzymes: oxidized form reduced form FAD FADH 2 NAD + NADH

O R – CH 2 – CH 2 – C - OH O R – CH 2 – CH 2 – C - SCoA CoASH - H 2 O O R – CH = CH – C - SCoA NAD + NADH OH O R – CH – CH 2 – C - SCoA H2OH2O water addition (Markovnyikov rule) FAD FADH 2 O O R – C – CH 2 – C - SCoA O R – C - OH O CH 3 – C - SCoA + instable compound in water decays immediately H2OH2O acetil-koenzyme A carbon chain is built backwards by the program of microorganism using this unit In case of energy demand: citric acid cycle  carbon dioxide and water

BIOLOGICAL DEGRADATION OF ORGANIC COMPOUNDS 1.Long chain carbon compounds (number of carbon atoms > ≈ 32): poorly decomposable or remains intact. This form is not favored by energetically This form has lower energy ? ? microorganism doesn’t find the end of chain Some bacteria have exocellular chain splitting enzymes. Short-term gains, the chain terminal disappears in ball.  plastic degradation is very slow in nature

2. Branched carbon chain compounds: no or slow degradation O R – CH – CH 2 – C – OH CH 3 O R – CH – CH 2 – C – SCoA CH 3 CoASH - H 2 O OH O R – C – CH 2 – C – SCoA CH 3 H2OH2O water addition (Markovnyikov rule) FAD FADH 2 O R – C = CH 2 – C – SCoA CH 3 O O R – C – CH 2 – C – SCoA CH 3 Motor oils contain mainly branched hydrocarbons, so the effect on environment is long-term.

3. Aromatic compounds: aromatic ring slowly, but biologically degradable O OH COOH CH 3 – COOH O O HO – C – C – CH 2 - COOH + cytochrom P-450 COOH OH cytochrom P-450

4. Highly condensed aromatic ring: not degradable Carcinogenic compounds containing highly condensed aromatic rings decay a few hours in atmosphere (sunshine), but toxic effect takes a long time in water and soil.

ORGANIC MATTER CONTENT OF WATER, BOD AND COD BOD (Biological Oxygen Demand) The oxygen quantity in a unit of water, necessary for the biological oxidation of organic matter during 5 or 20 days, at 20 °C Unit of BOD 5 or BOD 20 [mg oxygen/dm 3 ] BOD 5 necessary oxygen quantity for the biological oxidation of organic carbon compounds BOD 20 necessary oxygen quantity for biological oxidation of organic carbon and nitrogen compounds degradation of nitrogen compounds starts later organic nitrogen-containing compounds desamination NH ,5 O 2 H 2 O + 2 H + + NO 2 - NO ,5 O 2 NO 3 - NH 3 Nitrosomonas Nitrobacter In aqueous medium slow fast day BOI

ORGANIC MATTER DEGRADATION IN NATURAL WATERS approximated by first-order reaction BOD t = BOD 0 *(1 – e -kt ) BOD t : residual oxygen demand at the t time, BOD 0 : total biological oxygen demand at the beginning t=0 k : air supply constant at a given temperature Air supply constant water type k [day -1 ] 20°C Little lakes, dead branches 0,1 – 0,23 Slow flow 0,23 – 0,35 Large, slow water flow 0,35 – 0,46 Large, normal water flow 0,46 – 0,69 Fast flow 0,69 – 1,15 Conversion to other temperature: k(T) = k(20°C)*1,024 T-20

COD (Chemical Oxygen Demand) The oxygen quantity in a unit of water, necessary for the chemical oxidation of all dissolved or suspended organic matter by a strong oxidizer (potassium dichromate or potassium permanganate). The final product of the oxidation : CO 2 and H 2 O. Unit of COD [mg oxygen/dm 3 ] Relationship between BOD and COD BOD < COD General relationship, the chemical oxidizer disintegrates all organic compounds, but the microorganisms are choosy. BOD = COD Water sample contains only biologically degradable organic compounds. BOD << COD Water sample may contain toxic compounds or only small amount of biologically degradable organic matter.

SIMPLIFIED AEROB BIOLOGICAL WASTEWATER TREATMENT Accelerated biological degradation of organic matters by activated sludge in continuous aerobic fermenting tanks. anoxic basin: a.) pre-degradation of organic matters b.) ammonification (organic nitrogen → ammonia) c.) denitrification of recycled purificated wastewater (nitrate → nitrogen) aerobic basin: a.) air supply b.) oxidation of organic carbon c.) ammonia (formed in anoxic basin) oxidation to nitrate d.) increase of sludge mass

AEROB BIOLOGICAL WASTEWATER TREATMENT

SIMPLIFIED ANAEROB BIOLOGICAL WASTEWATER TREATMENT Accelerated biological degradation of organic matters by activated sludge in continuous anaerob fermenting tanks.

COMPARISON OF WASTEWATER TREATMENT TECHNOLOGIES organic matter content of waste water (100%) carbon content In form of carbon dioxide (~50%) carbon content of sludge ~50% carbon content of drain water ~ 1% organic matter content of waste water (100%) carbon content of biogas % methane : carbon dioxide ~ % carbon content of drain water ~ 1-5% carbon content of sludge ~1-5% AEROB ANAEROB - well known technology - lesser-known technology - aeration: energy intensive - large body of water –> warming problem - sludge disposal problem (heavy metals) - less sludge formation - sludge fermentation → biogas - fuel gas formation - sludge incineration - sensitive to toxic matter (ash content: 2000 mg/dm 3 (organic matter: > 25%) - higher capacity (water content: < 50 %) - 1 kg organic matter ~ 1 m 3 biogas