title: Evaluating sedimentation problems in activated sludge treatment plants operating at complete sludge retention time.
abstract: Zero net sludge growth can be achieved by complete retention of solids in activated sludge wastewater treatment, especially in high strength and biodegradable wastewaters. When increasing the solids retention time, MLSS and MLVSS concentrations reach a plateau phase and observed growth yields values tend to zero (Yobs ≈ 0). In this work, in order to evaluate sedimentation problems arised due to high MLSS concentrations and complete sludge retention operational conditions, two identical innovative slaughterhouse wastewater treatment plants were studied. Measurements of wastewaters' quality characteristics, treatment plant's operational conditions, sludge microscopic analysis and state point analysis were conducted. Results have shown that low COD/Nitrogen ratios increase sludge bulking and flotation phenomena due to accidental denitrification in clarifiers. High return activated sludge rate is essential in complete retention systems as it reduces sludge condensation and hydraulic retention time in the clarifiers. Under certain operational conditions sludge loading rates can greatly exceed literature limit values. The presented methodology is a useful tool for estimation of sedimentation problems encountered in activated sludge wastewater treatment plants with complete retention time.
authors.affiliation: Environmental Chemistry and WasteWater Treatment Lab, Environmental Engineering Pollution Control Department, Technological Education Institute of Western Macedonia, Koila, Kozani 50100, Greece. Electronic address: eAmanatidou@teiwm.gr.
authors.forename: Elisavet
authors.initials: E
authors.lastname: Amanatidou
authors.affiliation: Environmental Chemistry and WasteWater Treatment Lab, Environmental Engineering Pollution Control Department, Technological Education Institute of Western Macedonia, Koila, Kozani 50100, Greece.
authors.forename: Georgios
authors.initials: G
authors.lastname: Samiotis
authors.affiliation: Environmental Chemistry and WasteWater Treatment Lab, Environmental Engineering Pollution Control Department, Technological Education Institute of Western Macedonia, Koila, Kozani 50100, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Trikoilidou
authors.affiliation: Environmental Chemistry and WasteWater Treatment Lab, Environmental Engineering Pollution Control Department, Technological Education Institute of Western Macedonia, Koila, Kozani 50100, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Pekridis
authors.affiliation: Mechanical Engineering Department, Technological Education Institute of Western Macedonia, Koila, Kozani 50100, Greece.
authors.forename: Nikolaos
authors.initials: N
authors.lastname: Taousanidis
mesh_terms: D006112:Gravitation; D012212:Rheology; D012722:Sewage / Q000737:chemistry*; D013997:Time Factors; D014865:Waste Disposal, Fluid; D062065:Wastewater / Q000737:chemistry; D018508:Water Purification / Q000379:methods*
chemical_list: D012722:Sewage; D062065:Wastewater
keywords: Activated sludge; Complete sludge retention; Floc trapped nitrogen; Sedimentation problems; Sludge flotation; Zero net biomass