4.6 Physical, biological and chemical treatment processes microbial decomposition, predation, uptake in plants Biological ~ Physical ~ screening and filtration, sedimentation, flotation Learning objective: to become familiar with basic functions of various physical, chemical and biological processes. Chemical ~ coagultation/flocculation, adsorption, precipitation, UV-radiation What compounds can be removed from wastewater? How can Nature assist or react?

Treatment results for small and large water utilities More than 2,000 persons Treatment results for small and large water utilities Less than 2,000 persons J-O Drangert, Linköping University, Sweden 2

Possible combinations of physical processes B: Physical processes flotation and sedimentation screening filtration forced micro- filtration Possible combinations of physical processes Jan-Olof Drangert, Linköping university, Sweden 3

Screening of debris and other solid items Organics from kitchen pipe sorted out in a plastic screen Solids trapped by a screen in a city wastewater treatment plant Jan-Olof Drangert, Linköping university, Sweden 4

Flotation and sedimentation processes Inspection hole Baffels Inlet of wastewater Outlet of treated water Floating grease, particles, organisms Sludge built up Jan-Olof Drangert, Linköping university, Sweden

Filtration – mainly by gravity Partially unsaturated flow Saturated flow of wastewater Jan-Olof Drangert, Linköping university, Sweden 6

Forced micro-filtration Manufactured porous material Applied pressure Direction of filtered water flow Jan-Olof Drangert, Linköping university, Sweden

C: Chemical processes Adsorption of charged particles Adsorption of phosphate on ferric hydroxide OH H2PO4- + Fe OH H2PO4- + Al Adsorption of phosphate on aluminium hydroxide particles G. Jacks, Royal Institute of Technology, Stockholm 8

Adsorption of charged particles to soil medium The three important kinds of charged soil particles are: Organic matter RCOOH < > RCOO- + H+ (a negative pH-dependent charge) R is phenolic ring derived from lignite in residues of plants 2. Clay minerals Clay mineral consist of Al-Si-sheets with different cations (Na+, K+ etc.) in between the sheets. There is a negative charge on sides and edges: 3. Ferric hydroxides Fe(OH)3 < > Fe(OH)2- + H+ (a pH-dependent positive charge) R-COO- Pb 2+ R-COO- Mineral grain Organic ”overcoat” on a soil mineral Cu 2+ - - K+ K+ Mg 2+ - - - OH Fe(III) + HAsO4- G Jacks, Royal Institute of Technology, Stockholm 9

Adsorption of chemical compounds differ Copper (Cu) and Zink (Zn) are positively charged, and adsorb easily on organic matter and clays when the pH > 7 Arsenic (As) is negatively charged and adsorbs easily on ferric hydroxides when pH < 7 G Jacks, Royal Institute of Technology, Stockholm 10

Precipitation and flocculation Precipitation – a chemical reaction between dissolved compounds to form solids Flocculation - an aggregation process (or processes) leading to the formation of larger particles from smaller particles + - - + - + + G. Jacks, Royal Institute of Technology, Stockholm 11

UV-radiation by sunlight Inactivation of micro-organisms by UVA-radiation and increased temperature http://www.sodis.ch/Text2002/T-TheMethod.htm Source: Ubomba-Jaswa et al. 2009

Vertical view of the pond Shallow ponds with a dense population of algae More diffuse stratification Vertical view of the pond Strong algal stratification Courtesy of Duncan Mara, University of Leeds, UK K Tonderski, Linköping University Sweden

Ozonation and chlorination

D: Biological processes Karin Tonderski, Linköping university, Sweden 15

Biological processes - with air Oxygen is vital for most living organisms, including bacteria and viruses. When oxygen is present, organic matter (measured as BOD) is efficiently decomposed by organisms into CO2 + water: Unsaturated soil profile Organic matter Aerobic bacteria + oxygen Jan-Olof Drangert, Linköping university, Sweden 16

Biological processes - without air Many microorganisms can survive in environments with no oxygen and they use other compounds for their survival: Organic matter in waste-water + e.g. nitrate, sulphate or iron ions (Fe 3+ ) Anaerobic micro-organisms Saturated soil profile with little or no oxygen CO2 + e.g. N2, S2-, Fe2+ Jan-Olof Drangert, Linköping university, Sweden 17

Microorganisms attached to surfaces are more stable than those suspended in water wastewater flow anaerobic biofilm Biofilm o aerobic biofilm Grain particle Jan-Olof Drangert, Linköping university, Sweden

“Redox-ladder” When microorganisms descend the redox-ladder they first use O2 as an electron acceptor, then nitrate NO3, and further down other compounds as electron acceptors. The blue arrow indicates a reaction with energy-rich organic substances (electron donors) in the wastewater O2 H2O (oxygenisation) NO3- N2, N2O (denitrification) MnO2 Mn2+ Fe(OH)3 Fe2+ SO42- H2S (sulphate-reduction) CO2 CH4 (methanogenesis) Decrease in oxygen Gunnar Jacks, Royal Institute of Technology, Stockholm 19

Changes in concentrations of electron acceptors when organic matter (TOC) decomposes Exemplet från soptipp Gunnar Jacks, Royal Institute of Technology, Stockholm

What happens in the root zone? Water, nutrients, heavy metals, gases (e.g. CO2) O2, sugars, proteins, etc Organic matter, O2, NO3- , SO42-, CO2 etc Jan-Olof Drangert, Linköping university, Sweden 21

Predation on microorganisms stimulates decomposition Courtesy of Frida Lögdberg, Linköping university

Soil organisms vary tremendously in size and numbers A teaspoon soil ~ one gram Modified from Sylvia, D. et al. 2004. Principles and applications of soil microbiology

Organic matter is decomposed most efficiently in the top soil Million organisms per gram soil Anaerobic bacteria Aerobic bacteria Soil surface 106 106 Depth in meter 0.5 m Courtesy of G. Jacks, Royal Institute of Technology, Stockholm 24