Characterization of pig slurry with reference to flocculation and separation

Christensen, Morten Lykkegaard; Hjorth, Maibritt; Keiding, Kristian

doi:10.1016/j.watres.2008.11.010

Cited by 84 publications

(62 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Approximately 70% of the N in slurry is dissolved and most of the dissolved N is present as NH + 4 (Christensen et al, 2009). The NH + 4 in slurry, as well as in the liquid and solid separation fractions, may be lost due to volatilization as NH 3 (pKa = 9.25) or after microbial transformation as nitrous oxide or N 2 (Hansen et al, 2006).…”

Section: Nitrogenmentioning

confidence: 99%

See 1 more Smart Citation

Solid—liquid separation of animal slurry in theory and practice. A review

Hjorth

Christensen

et al. 2010

Agron. Sustain. Dev.

335

235

View full text Add to dashboard Cite

-Animal slurry contains plant nutrients that are essential for crop production. However, intensive livestock production may lead to a surplus of plant nutrients on farms and, as a consequence, discharge or emission to the environment. In order to ensure that the slurry applied to fields matches the nutrient requirements of the crops, techniques have been developed to reduce the nutrient content of slurry by means of separation. This review discusses the separation technologies used for animal slurry treatment and the physical and chemical processes involved in separation. These processes need to be understood before efficient, reliable and cheap separation technologies that take into account the actual properties of slurry and the likely end-use of the separation products can be developed. A simple separation efficiency expression can be used to assess the efficiency of slurry separation. It is indeed important to measure the amount and composition of the slurry before treatment, the dry-matter-rich fraction and the liquid fraction. The separation efficiency of mechanical separators for the removal of dry matter and phosphorus (P) is ranked as follows: centrifugation > sedimentation > non-pressurized filtration > pressurized filtration. In general, the separation of total N and NH + 4 follows the same pattern, but the separation efficiency is lower than for dry matter and P. Treatment with a flocculant before separation improves separation efficiency significantly. Of the polyacrylamide polymers tested, high-molecular-weight, linear cationic polymers with a medium charge density (20-40 mol%) were found to be the most efficient flocculants. The best mechanical separation techniques for flocculated slurry are screens or filter belts. The separation efficiency of polyacrylamide-treated slurry can be improved by adding a multivalent ion to coagulate particles and for precipitation of phosphorus. Aluminium sulfate (Al 2 (SO 4 ) 3 ) or ferric chloride (FeCl 3 ) seem to be very efficient for improving the mechanical separators. Alternatively, the mineral struvite (MgNH 4 PO 4 ) may be formed by changing the slurry characteristics, such as by the addition of magnesium (Mg) or by increasing the pH to 9. The struvite crystals are removed during solid-liquid separation. The products of the solid-liquid separation may be further treated by evaporation, membrane filtration or ammonia stripping in order to obtain the desired end-products; however, low-maintenance and/or cost-efficient operation of these post-treatments has not yet been demonstrated. The separation should be developed as a whole-system approach, paying attention to parameters such as the value of end-products, environmental consequences and economy.

show abstract

Section: Nitrogenmentioning

confidence: 99%

“…The orthophosphate fraction may vary during storage, i.e. increase immediately after excretion and reach a maximum, and thereafter it will decrease slightly (Christensen et al, 2009). …”

Section: Phosphorusmentioning

confidence: 99%

Solid—liquid separation of animal slurry in theory and practice. A review

Hjorth

Christensen

et al. 2010

Agron. Sustain. Dev.

335

235

View full text Add to dashboard Cite

show abstract

“…An acidic pH moves the chemical equilibrium and increases availability of phosphate ions (HPO4 2-→ PO4 3-), which generally increase solubility of P complexes (since P is limiting ion for precipitation), while alkaline pH results in P-precipitation as Mg-P or Ca-P based compounds (Sommer and Husted 1995, Nelson, Mikkelsen et al 2003, Burton 2007, Christensen, Hjorth et al 2009). Struvite solubility is lowest between pH 8 and 10, as shown in the Fig.…”

Section: Phmentioning

confidence: 99%

Enhanced phosphorus solubility during anaerobic digestion

Latif¹

View full text Add to dashboard Cite

Worldwide phosphorus (P) consumption has increased massively over the last century, to overcome soil nutrient constraints, and to feed an increasing population with an increasing level of urbanization.However, current P reserves are limited and are expected to deplete in 50-120 years. Hence, new techniques to source P from alternative resources are essential. Waste streams are the largest alternative resource of P, with much of the organic wastes containing P treated by anaerobic digestion (AD). However, P recovery from the digested waste streams is limited by in-reactor P precipitation, and inaccessibility of soil available P in sludge biosolids. In-reactor P precipitation increases the operational costs of a treatment facility due to scaling and precipitation, there are strong advantages in being able to recover P as a purified mineral product. In such circumstances, keeping high PO4 concentration during AD is vital to enhance its recovery post AD.This thesis aims to assess two different techniques to enhance PO4 concentration during AD from waste activated sludge (WAS): low pH and high pressure (enabling low pH). Low pH single stage AD was tested in both batch and continuous mode. In the batch study, biochemical methane potential tests were conducted for 51 days at a pH range of 5.0 to 7.2 in two separate sets (two different WAS samples collected from municipal WWTP). Low pH (< 5.7) caused a significant loss in the methane potential (B0) of up to 33%, with 3.6 times increase in PO4 concentration compared to the neutral pH (7 -7.7), but with no major change in methane production rate coefficient (khyd). The loss in methane yield was mainly due to decrease in hydrolytic capability rather than inhibition of methanogenesis with volatile fatty acids (VFAs) being < 300 mgCOD L -1 and soluble COD < 1300 mgCOD L -1 even at low pH. While pH did not influence the acetoclastic community (Methanosaeta dominated), it was the primary driver for the remaining community, and caused a loss of diversity and shift to Clostridia.To validate the results from batch conditions, continuous low pH AD was performed using similar substrate and pH conditions. The influence of the pH on PO4 concentration was similar in continuous and batch. It was found that the low pH (5.5) caused a significant increase in PO4 concentration up to 79% of the total P, while methane yield was reduced by 50%. VFAs and SCOD concentrations increased from 40 to 504 mg L -1 and 600 to 2017 mg L -1 respectively, as the pH was reduced from 7.0 to 5.5. Higher concentration of propionic acid (370 -430 mg L -1 ) was recorded at low pH (< 5.5).The reduction in methane yield was associated with a shift in microbial community and decreased destruction of particulate organics. Acidogens dominated at low pH (< 6.0), while methanogens decreased by 88% at pH 5.5 compared to neutral pH. Apart from the loss in methanogenic and hydrolytic capacity, continuous acid dosing to maintain low pH condition was identified as a key limitation with this technology. To assess an...

show abstract

“…In regards to AD on phosphorus availability, discussions are very discrepant among studies. While some state that this degradation process increases the nutrient availability for plants [6] or that it does not have direct effects [7], some state that AD has potentially the opposite influence, i.e., it decreases P availability for plants [8][9][10]. It is known that pH influences the solubility of P and micronutrients; e.g., raising the pH moves the chemical equilibrium toward the formation of dissociated phosphate ion, which facilitates the precipitation of such ion as insoluble Ca and Mg phosphates.…”

Section: Anaerobic Digestionmentioning

confidence: 99%

“…This mechanism can be especially useful because it is well accepted that the majority of manure phosphorus already exists in the colloidal form rather than dissolved phosphate anions, so crystallization of phosphate salts may be unnecessary prior to coagulation. Precipitation of insoluble phosphate salts, e.g., FePO 4 and Fe 5 (PO 4 ) 2 (OH) 9 when ferric is added, is another significant factor contributing to phosphate removal [48]. When chemical dosing is high, insoluble metal hydroxides are precipitated from liquid, which will also enmesh particulate materials by a sweep action.…”

Section: +mentioning

confidence: 99%