Thesis-2000-CarliellMarquet.pdf (62.63 MB)
The effect of phosphorus enrichment on fractionation of metals and phosphorus in anaerobically digested sludge
thesis
posted on 2015-03-23, 10:57 authored by Cynthia Carliell-MarquetIn designated nutrient-sensitive areas, phosphorus must be removed from sewage
before it is discharged to the receiving water body. Phosphorus-rich sludge is
generated, which is usually digested anaerobically prior to disposal. This research
investigated the effect of phosphorus enrichment on metal and phosphorus
fractionation in anaerobically digested sludge. The use of two complementary
sequential chemical extraction procedures to measure phosphorus and metal
fractionation, was a key focus of the research. The fractionation procedures were
tested by sequentially extracting inorganic compounds (phosphates, sulphides and
carbonates) which showed that the operationally defined metal and phosphorus
fractions were not always representative of precise metal phases. Species were
tentatively assigned to metal and phosphorus fractions using model compound results.
Laboratory-scale batch anaerobic digestion experiments were performed, in which
model compounds were used to simulate conditions of soluble and insoluble
phosphorus enrichment. Soluble phosphorus at concentrations of 500 mg/l or greater
was found to retard volatile solids removal and methane production in the laboratory
digesters. Soluble phosphorus enrichment facilitated precipitation of calcium,
magnesium and manganese but increased trace metal solubility, particularly that of
chromium. Enrichment of digesters with Na2HP04 and MgCb caused struvite to
precipitate in digesters containing 1000 mg/l of additional phosphorus. FeP04
enrichment of digested sludge showed that ferric iron was reduced to ferrous iron,
releasing soluble phosphorus into the digester. Most of the phosphorus was reprecipitated
as ferrous phosphate, causing co-precipitation of magnesium, manganese
and cobalt. By contrast, A1P04 added to the digesters was stable in the sludge. Full-scale
CPR sludge digestion (Fe2(S04)3 dosing) caused soluble phosphorus in the
digester to decrease below 0.05 mg/l. Phosphorus remained associated with iron in the
sludge fraction but soluble calcium and magnesium concentrations in the full-scale
digester increased as a result of CPR sludge digestion. Comparison of laboratory and
full-scale results showed that the fate of iron-precipitated phosphorus in digested
sludge was primarily dependent pn the molar ratio of Fe:P in the sludge. Full-scale
BPR sludge digestion showed high concentrations of soluble phosphorus in the
digester and some struvite precipitation, although phosphorus was precipitated
primarily as calcium phosphate, as was found to occur in the laboratory digesters
simulating BPR sludge digestion.
History
School
- Architecture, Building and Civil Engineering
Publisher
© Cynthia Carliell-MarquetPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/Publication date
2000Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.366554Language
- en