Iron salts are used at wastewater treatment plants (WWTPs) for several reasons: for removing chemical phosphorus, preventing from struvite formation and reducing the content of hydrogen sulfide (H2S) in biogas. Anaerobic digestion is a common scheme for sludge treatment due to producing biogas that could be used as biofuel. Laboratory analysis has been carried out using anaerobic digestion model W8 (Armfield Ltd, UK) to investigate any possible effect of adding FeCl3 on the anaerobic digestion of primary sludge (PS) and waste activated sludge (WAS) mixture as well as on releasing phosphates to digested sludge liquor. The obtained results showed that FeCl3 negatively impacted the anaerobic digestion process by reducing the volume of produced biogas. Fe-dosed sludge (max) produced 30% less biogas. Biogas production from un-dosed and Fe-dosed sludge (min) was similar to the average of 1.20 L/gVSfed. Biogas composition was not measured during the conducted experiments. Phosphorus content in sludge liquor increased at an average of 38% when digesting sludge without ferric chloride dosing. On the contrary, phosphate content in sludge liquor from digested Fe-dosed sludge decreased by approx. 80%. Santrauka Nuotekų valymo įrenginiuose geležies druskos naudojamos cheminiam fosforui šalinti, sieros vandeniliui biodujose mažinti ir struvito nuogulų formavimosi prevencijai. Tyrimai atlikti laboratorinėmis sąlygomis naudojant anaerobinio pūdymo modelį W8 (Armfield Ltd., Didžioji Britanija) ir pūdant pirminio perteklinio dumblo mišinį, į kurį buvo dedama geležies druskos, siekiant nustatyti geležies druskos naudojimo efektą anarobinio pūdymo procesui ir fosfatų išsiskyrimui į dumblo vandenį. Rezultatai parodė, kad pūdant dumblą be geležies druskos ir dedant geležies druskos minimalią dozę, susidarė vidutiniškai vienodi kiekiai biodujų (mL/gBSMtiekiam.), bet į pūdomą dumblą dedant maksimalią geležies dozę, biodujų išeiga vidutiniškai sumažėjo 30 %. Į pūdomą dumblą nededant geležies chlorido, fosfatų koncentracija dumblo vandenyje vidutiniškai padidėjo 38 %. Ir priešingai, geležies chlorido dozės fosfatų koncentraciją pūdyto dumblo vandenyje sumažino 80 %.
In this study, the impact of iron and aluminium salts addition on anaerobic digestion process was investigated. Mixture of primary and activated sludge collected at Vilnius wastewater treatment plant in Lithuania was digested under laboratory conditions by using anaerobic digester (W8, Amfield, UK). To compare the relative digestibility of iron-dosed (Fe-dosed) and aliuminium-iron-dosed (Al-Fe-dosed) sludge with un-dosed sludge three continuous experiments were made. Results showed that iron and aliuminium negatively impacted anaerobic digestion process by reducing the volume of biogas produced. Fe-dosed sludge produced 20-50% less biogas and Al-Fe-dosed sludge produced 30-40% less biogas in comparison to the same un-dosed sludge. VS destruction decreased during dosing of Fe or/and Al salt. Biogas composition was not measured during the experiments. KEYWORDSWastewater sludge (primary and activated sludge), lab-scale anaerobic digestion, aliuminium salt, iron salt, biogas production.
Ochre, waste iron sludge from the treatment of iron rich groundwater for potable use, makes up a significant waste problem. Furthermore, wastewater treatment plants with enhanced biological phosphorus removal and the digestion of sludge are in lack of iron for the prevention of hydrogen sulfide production and the release of phosphorous during anaerobic digestion. Thus, the addition of ochre to anaerobic digestion is a potential beneficial reuse of ochre. Sludge from wastewater treatment plants with enhanced biological phosphorus removal was used for the experiments. Batch and continuous pilot-scale tests were performed for the mesophilic digestion of primary and waste-activated sludge with different doses of ochre. Two different doses of ochre corresponding to molar ratios of 1 and 2 moles Fe 3+ /mole P released in the batch test resulted in 29% and 57% reductions of phosphates respectively in the sludge liquor compared to the control sludge without inhibiting the digestion process. In the pilot experiment, the dosing of ochre at both a high and low dose (molar ratios of 1.6 and 0.8 Fe 3+ /S 2− , respectively) resulted in an immediate drop in the H 2 S concentration (from >2000 ppm down to 570 ppm), while the control reactor still produced biogas with a high hydrogen sulfide concentration. The inhibition of the digestion process was observed (accumulation of acetate) at the higher dose. In a second pilot scale experiment, lower doses of ochre were tested continuously (1.5 and 0.75 mole Fe 3+ /mole P released ) to avoid any inhibition, while evaluating the phosphate precipitation. A reduction of phosphates in sludge liquor (33% and 66% for the low and high doses respectively) was obtained.
Tyrimų metu buvo nustatyta galimybė panaudoti geležies paplavas, gautas iš Antavilių vandens gerinimo įrenginių, fosfatams šalinti iš pūdyto dumblo vandens, paimto iš Šiaulių nuotekų valymo įrenginių, kuriuose vykdomas bio-loginis azoto ir fosforo šalinimas ir anaerobinis dumblo apdorojimas. Eksperimentui atlikti buvo naudojamas laboratorinis stendas su stikliniais l litro talpos indais ir maišyklėmis. Pradinė fosfatų koncentracija dumblo vandenyje buvo 55–72 mgPO4-P/l, geležies paplavų įterpimas 8 skirtingomis dozėmis – nuo 0,1 g/l iki 30 g/l į 15 min. maišomą dumblo vandenį – visa tai leido sumažinti fosfatų koncentraciją dumblo vandenyje. Geriausias rezultatas buvo gautas, įterpus 10 g/l geležies paplavų dozę, kai fosfatų šalinimo efektyvumas atitinkamai buvo 73,1±2,1 ir 65,0±0,9 % pirmojo ir antrojo bandymo metu. Optimaliausias maišymo laikas yra 15 min., kai fosfatų pašalinimo efektyvumas buvo 38,2 %.
The dissertation examines impact of iron salts and ochre (iron sludge from water treatment plant) on digestion of sludge mixture from wastewater treatment plants with biological phosphorus removal process. Research object was anaerobic digestion of sludge mixture with traditional and alternative iron sources added. The aim of work was to examine the potential of ochre as an alternative iron source and to investigate factors governing anaerobic digestion process: methane production rate, hydrogen sulphide removal process and reduction of internal phosphates recycling at wastewater treatment plants with biological treatment plants. Dissertation consists of introduction, three chapters, general conclusions and recommendations, references and list of author's publication on the topic of dissertation. In introduction main problem is discussed; topicality of work, object of research, aim and objectives of work are formulated, of the work are described; research methodology, scientific novelty of research, practical significance of results and defended propositions are presented. In the end of introduction author's articles, structure of dissertation and acknowledgements are presented. In the first chapter literature concerning with the studied topic is analysed. Information about sludge sources, types and characterisation, anaerobic digestion process and previous research on results on impact of aluminium and iron. In the end of chapter conclusions and tasks are reformulated. Second chapter presence methodologies used for the research. Laboratory and pilot-scale anaerobic reactors and characteristics of sludge and ochre used for the experiments are described. In third chapter results on impact of iron salts and ochre are presented and discussed, comparison with other researchers obtained results is made. Proposed technological scheme for use of ochre at the wastewater treatment plants with biological phosphorus removal presented and described. Ten articles have been published on the topic of thesis: two-in scientific journal referred in the other databases, two-in International Conference material, three-in Lithuanian Conference material. 12 presentations were made at the Republic and International Conferences and Seminars. vi Reziumė Disertacijoje nagrinėjama geležies druskų ir geležies paplavų (ochra) iš geriamo vandens paruošimo įrenginių įtaką dumblo pūdymo procesui. Tyrimo objektas-dumblo mišinio pūdymas, į jį įterpiant tradicinį arba alternatyvų geležies šaltinį. Pagrindinis disertacijos tikslas-ištirti geležies paplavų, kaip alternatyvaus geležies šaltinio, panaudojimo galimybes ir nustatyti faktorius, įtakojančius pūdymo proceso kokybę: metano susidarymą, sieros vandenilio pašalinimo procesą ir vidinės fosfatų recirkuliacijos sumažinimą nuotekų valymo įrenginiuose su biologiniu fosforo šalinimu. Disertaciją sudaro įvadas, trys skyriai, bendrosios išvados ir rekomendacijos, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašas. Įvadiniame skyriuje aptariami tiriamoji problema ir darbo aktualuma...
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