SEWAGE (wastewater) SLUDGE TREATMENT and DISPOSAL

primary settling tank (sedimentation and VFA production) secondary (final) settling tank activated sludge reactor (or trickling filter) grid chamber (screens) grit chamber (sand trap) treated wastewater (optionally to tertiary treatment) raw wastewater return sludge waste activated sludge (excessive sludge) 0,5 1 % TS primary sludge 1 2 % TS polymer dosage VFA in supernatant mechanical thickening gravity thickening mixed sludge 5  7 % TS drying and burning 20  40% TS stabilization (+ hygienization if thermophilic conditions) 3  5 % TS land disposal dewatering conditioning landfilling hygienization (pathogen inactivation) SEWAGE (wastewater) SLUDGE TREATMENT and DISPOSAL

SEWAGE SLUDGE VOLUMES AND COMPOSITION Sewage sludge production • 1-2 % of treated wastewater volumes • 0,5÷1,2 kg TS / kg BOD removed from ww • 0,273 kg TS / 1 m3 of treated wastewater Table 1. Sewage sludge composition Table 2. Pathogens in raw sewage sludge * ATT indicator represents the total number of viable eggs of helmints: Ascaris sp., Trichuris sp. and Toxocara sp. in 1 kg TS of sludge

SEWAGE SLUDGE VOLUMES AND COMPOSITION Table 3. Manurial value of sewage sludge and other fertilizers Table 4. Calorific value of different fuels,and sewage sludge

after dewatering after thickening SEWAGE SLUDGE TREATMENT AND DISPOSAL thickening stabilization and pathogen inactivation (hygienization) conditioning and dewatering disposal (land application, landfilling, drying and burning) Stages of sludge treatment and disposal Thickening and dewatering Unit operations used to increase the solids concentration of sludge and subsequently reduce its volume

SEWAGE SLUDGE THICKENING • gravity thickening • dissolved air flotation thickening • mechanical thickening – pressure filtration (centrifuges, belt thickeners) – vacuum filtration (rotary drum thickeners) SEWAGE SLUDGE DEWATERING MECHANICAL DEWATERING LAND DEWATERING • centrifuging • vacuum filtration • pressure filtration • drying beds • lagoons Mechanical processes require the sludge conditioning with organic polymers prior to dewatering!!! IMPORTANT !!!

BASIC TERMS - what are biosolids and stabilization? Nutrient-rich organic material produced from stabilization of sludge that meet specific quality criteria and are suitable for land application.(from - the biological processing of wastewater solids) BIOSOLIDS Formation of stable end products (CO2, CH4, H2O, inorganic solids, insoluble organic residues) that are relatively resistant to further biological activity and have characteristics similar to humus. STABILIZATION A breakdown of complex organic substances through the action of bacteria and other microorganisms. Digestion needn’t provide stable end products!!! DIGESTION A biological process providing to ATP reproduction in which organic substances serve as both electron donors and electron acceptors . FERMENTATION Conversion of biodegradable organic substances to VFAs, alcohols, aldehydes, CO2 etc. through the action of fermentative heterotrophic bacteria. ACID FERMENTATION

THE GOALS OF STABILIZATION STABILIZATION CAN BE ACHIEVED BY • reduction of TS and VS concentration in sludge, • elimination of organic compounds responsible for odor formation, • significant reduction of putrescibility, • partial or complete inactivation of pathogens. • biological action (anaerobic or/and aerobic bacteria) • chemical treatment (strong oxidants) • heating (drying or/and burning) • other methods that lead to VS reduction or transformations STABILIZATION PHYSICAL-CHEMICAL BIOLOGICAL • lime stabilization • heat treatment • anaerobic digestion (AD) • aerobic stabilization at ambient temperatures • Aerobic thermophilic digestion (ATAD) • composting

Organic polymers (proteins, fats, carbohydrates) HYDROLYSIS (solubilization) extracellular enzymes Organic soluble poly- and monomers (amino acids, fatty acids, monosaccharides) Facultative bacteria: Aerobacter, Clostridium, Escherichia, Streptococcus, Micrococcuss, Pseudomonas, Flavobacterium ACIDOGENESIS VFA (except formic and acetic) ethanol, aldehydes CO2, H2 Syntrophobacter, Syntrophomonas, Desulfovibrio ACETOGENESIS Clostridium, Acetobacterium, Acetogenium Acetates Formic acid, methanol Methane formers (Archaea): Methanobacterium, Methanobrevibacter, Methanococcus, Methanomicrobium, Methanospirillum,Methanosarcina, Methanothrix, Methanoghermus METHANOGENESIS CH4, CO2 Anaerobic decomposition of organic matter - biochemistry

ANAEROBIC DIGESTION – application: 1. Wastewater treatment plants - sewage sludge stabilization; 2. Anaerobic wastewater treatment (food industry); 3. Biogas plants – treatment (co-digestion) of organic wastes including: • organic fraction of municipal solid wastes; • fruit ,vegetable wastes; • leaves, grass and plant residues, corn and hay silage; • pig, poultry and dairy manure • slaughterhouse wastes

Yield and composition of biogas from sewage sludge AD: • 0.3-0.5 m3/kgVSfed • 0.8-1.1 m3/kgVSreduced • CH4 = 65-75 % • CO2 = 25-35 % • trace gases (N2, H2S, O2, and others) < 1 %

Anaerobic digestion tanks for sludge stabilization source: Li Y.Y.,Mizuno O., Miyahara T., Noike T., 1997. Katsumata K., Ecological analysis of the bacterial system in a full-scale ecc-shaped digester treating sewage sludge, Water Science Technology, vol. 36, no. 6-7, pp. 471-478.

Conventional AD tanks for sludge stabilization

Egg-shaped AD tanks for sludge stabilization

Anaerobic wastewater treatment • mainly used to treat high contaminated wastewater (COD > 400 g/m3); • application – any organic wastewater e.g. liquid manure, food industrial ww etc. • no aeration required; • low sludge production (excess biomas = 2 – 6 % CODremoved; 10-times lower than for AS); • biogas yield – around 0.3-0.4 m3/kgCODremoved • only partial biodegradation of organics (up to 70 % of BOD removal) can be achieved – additional treatment need to be provided (AS, TF); • great sensitiveness – operating problems might occur; • operated at ambient conditions – long SRT. Reactors for anaerobic wastewater treatment: conventional digester without recycle digester with recycle upflow/downflow fixed film reactor fluidized bed reactor (FBR) and expanded granular sludge bed reactor (EGSB) upflow anaerobic sludge blanket (UASB)

Reactors for anaerobic wastewater treatment

1. Conventional digester with no recycle • non-ideal CSTR or batch reactor; • HRT = 10-30 d at 35 0C; up to 4 months at ambient temp. • the only method to control SRT is to limit the influence flow rate; • influent COD = 15 – 180 g/dm3. 2. Digester with recycle - contact process • well-mixed reactor with recycle, • SRT can be controlled separately from HRT, HRT can be considerably reduced, • suitable for intermediate TSS concentrations 10-20 g/dm3, COD = 2-100 g/dm3, • influent quality can be poor because of recycle (fixed film reactors more attractive), • HRT = 1-7 d, SRT the same as for the conventional process.

3. Upflow fixed film reactor (anaerobic filter) • a fixed (stationary) medium provides a surface on which bacteria attach and growth. It accounts for 60-90 % of Vreactor • rocks or plastic modules used as media – large specific surface area but clogging problems (void volumes > 50 %) ; • both attached and suspended (in clumps) growth is provided; • as a consequence of this, SRT = 100 d can be achieved; • relatively high quality effluent; BOD removal = 60-70 %. • very long acclimation period – a few months, but lower sensitiveness than UASB; • HRT = 1 d usually sufficient; • good filtration capacities (but clogging problems) 3a. Downflow fixed film reactor (thin film reactor) • wastewater flows downward through several vertically oriented clay tubes (d=5-10 cm); • bacteria and methanogens are grown inside channels to the thickness of 1-3 mm; • less subject to plugging because larger channels are provided in media;

4. Fluidized bed reactor (FBR) and expanded granular sludge bed reactor (EGSB) • bacteria are grown on movable medium particles (e.g. sand, quartzite, anthracite, granular activated carbon) as the ww is pumped upward through reactor at a high rate – this limits growth of bacterial biofilm to small thickness; • solid phase represents 10-20 % of the Vreactor (by weight) for EGSB, and up to 40 % for FBR; • recirculation of the treated wastewater needed; • recommended media size = 0.1-1.0 mm in diameter; • bed expansion reduces clogging potential, and provides more surface area for biofilm (high biomass density) – more treatment capability and shorter HRTare attained. • typical influent COD = 1 – 30 kg/m3; HRT = 6 – 24h. • Successful for low influent COD!!! (< 600 g/m3) EGSB reactor

5. Upflow anaerobic sludge blanket reactor (UASB) • invented in the NL by prof. Letting, most commonly used for high rate anaerobic ww treatment; • development of a dense, active granular sludge mass in the lower portion of reactor – sludge bed, and sludge blanket zones; • sludge granulesd = 0.14–5 mm, sometimes flocculents – consist of mineral core (10-90 % by weight), internal anaerobic layer with methanogens, and external anoxic/aerobic layer with acidogenic and acetogenic bacteria (including filamentous forms); • liquid upper zone and gas-liquid-solid separator – important to the success of the reactor; • very sensitive process – several days or even weeks of acclimation; • capable to treat high concentrated wastewater – COD = 0.5 – 20 kg/m3, • HRT = 0.3 – 5.0 d.

SEWAGE (wastewater) SLUDGE TREATMENT and DISPOSAL