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1.
Environ Technol ; : 1-10, 2019 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-31750797

RESUMO

Nutrients were extracted from digester supernatant sampled from a full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plant. A four-compartment selectrodialysis setup was used to extract ammonium and phosphate in two separate compartments. The initial phosphate recovery rate was measured to be 0.072 mmol m-2 s-1 and the initial ammonium recovery rate was measured to be 1.31 mmol m-2 s-1. The ammonium recovery rate was 18 times higher than that for phosphate, whereas the molar concentration of ammonium in the feed was 10 times higher than that of phosphate. An average recovery of 72 ± 1% and 90 ± 10% for ammonium and phosphate was observed after 3 h of operation. A monovalent anion selective (MVA) membrane was used to avoid ammonium and reduce the concentration of monovalent anions in the phosphorus stream. The pH in the phosphorus stream was kept at 10 so phosphate did not pass the MVA membrane. A membrane area of 26 m2 per m3 digester supernatant was required to recover 70% of phosphate and ammonium for the digester supernatant that contained 6 mM phosphate and 105 mM ammonium.

2.
Chemosphere ; 236: 124299, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31323551

RESUMO

The mechanical dewatering of sludge is important in order to achieve a high dry matter content, thereby lowering the transportation cost and the energy consumption during incineration. Thermogravimetric analysis is sometimes used to estimate the maximum dry matter content obtainable from mechanical dewatering, by measuring the critical moisture point. In this paper, the critical moisture point of digested sludge was measured and compared with vapour sorption curves. The critical moisture point was determined for raw and conditioned sludge to be 3.4 kg of water per kg of dry matter, corresponding to 23% w/w dry matter. This value was lower than the dry matter content obtained from the mechanical dewatering process, indicating that the dry matter content can exceed the critical moisture point. Moisture vapour sorption was measured for raw, conditioned, and dewatered sludges. The Blahovec and Yanniotis sorption isotherm fitted the experimental data well. Between 10 and 12 g of water was adsorbed as a monolayer per 100 g of dry matter. The rest of the moisture content was explained by the non-ideal Raoult's law, by including the effect of dissolved ions. At water activities above 0.95, the moisture content was determined by capillary condensation and cake compressibility. The water activity was higher than 0.95  at the critical moisture point and the capillary pressure was estimated to be 4-6 bars. This pressure was responsible for cake compression during drying, while the relatively low dry matter content at the critical moisture point may be due to the low capillary pressure.


Assuntos
Dessecação , Gases/análise , Esgotos/química , Vapor/análise , Íons , Termogravimetria , Pressão de Vapor , Água
3.
Environ Technol ; : 1-7, 2019 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-30806590

RESUMO

Phosphorus recovery from wastewater is a focus area in Denmark; the aim is to recover at least 80% of the phosphorus. In order to extract phosphorus, surplus sludge from wastewater treatment plants was acidified (pH 2-4) to increase the dissolved phosphorus concentration, which then can be precipitated and recovered. Pilot-scale acidification and dewatering tests were done using sludge from three different wastewater treatment plants: plant (1) digested primary and secondary sludge, plant (2) digested primary sludge, and plant (3) non-digested sludge. Treatment of digested sludge gave the highest phosphorus release, but the acid consumption was high due to carbon dioxide stripping. The dry matter content of the acidified dewatered sludge was high (20-40%), but the dry matter content in the filtrate increased with decreasing pH. Approximately half of the dry matter content in the filtrate could be removed by introducing an additional separation step. The optimal pH for phosphorus extraction was 3, where up to 68% of the phosphorus was dissolved. Part of the released orthophosphate was lost with the filter cake but still, 60% of the total phosphorus content in the sludge ends up in the filtrate.

4.
Water Res ; 146: 307-317, 2018 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-30292955

RESUMO

Acidification was used to dissolve phosphorus from digested and non-digested sludge from five wastewater treatment plants in order to make phosphorus accessible for subsequent recovery. More phosphorus was dissolved from digested sludge (up to 80%), with respect to non-digested sludge (∼25%) and the highest release was observed at pH 2. The acid consumption for digested sludge was higher than for non-digested sludge due to the presence of the bicarbonate buffer system, thus CO2 stripping increased the acid consumption. In all the experiments, the sludge was exposed to acid for 1 h. For the five tested sludge types, 60-100 mmol o-P was released per added mol H2SO4. It was mainly iron and calcium compounds that accounts for the phosphorus release at low pH. The release of heavy metals was in general low (<30%) for all the wastewater treatment plant, as Zn, Cd and Ni showed the most critical release after acidification of non-digested sludge.


Assuntos
Metais Pesados , Esgotos , Concentração de Íons de Hidrogênio , Ferro , Fósforo
5.
Water Sci Technol ; 77(3-4): 748-758, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29431720

RESUMO

The technical performance of a precoat filter was compared with that of a traditional sand filter. Particle concentration and size distribution were measured before and after the filtration of swimming pool water. Both the sand and precoat filters could reduce the particle concentration in the effluent. However, higher particle removal efficiency was generally observed for the precoat filter, especially for particles smaller than 10 µm in diameter. Adding flocculant improved the removal efficiency of the sand filter, resulting in removal efficiencies comparable to those of the precoat filter. Three powders, i.e., two types of perlite (Harbolite® and Aquatec perlite) and cellulose fibers (Arbocel®), were tested for the precoat filter, but no significant difference in particle removal efficiency was observed among them. The maximum efficiency was reached within 30-40 min of filtration. The energy required for the pumps increased by approximately 35% over a period of 14 days. The energy consumption could be reduced by replacing the powder on the filter cloth. The sand filter was backwashed once a week, while the powder on the precoat filter was replaced every two weeks. Under these conditions, it was possible to reduce the water used for cleaning by 88% if the precoat filter was used instead of the sand filter.


Assuntos
Filtração/métodos , Piscinas , Purificação da Água/métodos , Óxido de Alumínio/química , Celulose/química , Conservação dos Recursos Naturais , Floculação , Tamanho da Partícula , Dióxido de Silício/química
6.
PLoS One ; 12(7): e0181652, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28749990

RESUMO

A filtration devise was developed to assess compressibility of fouling layers in membrane bioreactors. The system consists of a flat sheet membrane with air scouring operated at constant transmembrane pressure to assess the influence of pressure on resistance of fouling layers. By fitting a mathematical model, three model parameters were obtained; a back transport parameter describing the kinetics of fouling layer formation, a specific fouling layer resistance, and a compressibility parameter. This stands out from other on-site filterability tests as model parameters to simulate filtration performance are obtained together with a characterization of compressibility. Tests on membrane bioreactor sludge showed high reproducibility. The methodology's ability to assess compressibility was tested by filtrations of sludges from membrane bioreactors and conventional activated sludge wastewater treatment plants from three different sites. These proved that membrane bioreactor sludge showed higher compressibility than conventional activated sludge. In addition, detailed information on the underlying mechanisms of the difference in fouling propensity were obtained, as conventional activated sludge showed slower fouling formation, lower specific resistance and lower compressibility of fouling layers, which is explained by a higher degree of flocculation.


Assuntos
Reatores Biológicos , Filtração/instrumentação , Incrustação Biológica , Floculação , Membranas Artificiais , Pressão , Esgotos , Águas Residuárias/análise , Purificação da Água
7.
Water Res ; 120: 117-132, 2017 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-28478289

RESUMO

A range of parameters affecting floc characteristics, sludge composition and filtration properties was investigated by analyzing 29 sludge samples from municipal and industrial conventional activated sludge systems and municipal membrane bioreactors (MBR). Samples were characterized by physico-chemical parameters, composition of ions and EPS, degree of flocculation, settling properties, dewatering properties, and filtration properties. By analyzing the interplay between various metrics instead of single parameters, a unified understanding of the influence of sludge composition and characteristics was developed. From this, a conceptual model was proposed to describe the interplay between sludge composition, characteristics, and filtration properties. The article shows three major results contributing to describe the interplay between sludge characteristics and fouling propensity: First, the degree of flocculation could be quantified by the ratio between floc size and residual turbidity and was a key parameter to assess fouling propensity. Second, extracted EPS to polyvalent cations ratio was used as an indicator of the flocculation. A high ratio combined with a high concentration of EPS resulted in large, loosely bound, and weak flocs that were easily deformed, hence giving compressible fouling layers. Finally, high amounts of carbohydrates in both total and extracted EPS resulted in more pronounced fouling, which may be explained by carbohydrates forming poorer flocs than humic substances and proteins. Accordingly, samples with high humic content showed lower specific resistance to filtration due to better floc structure. The amount of carbohydrates in EPS correlated positively to the influent COD/N ratio, which may explain why systems with high influent COD/N ratio demonstrated higher fouling propensity.


Assuntos
Floculação , Esgotos , Reatores Biológicos , Cátions , Filtração , Eliminação de Resíduos Líquidos
8.
Membranes (Basel) ; 6(4)2016 Dec 13.
Artigo em Inglês | MEDLINE | ID: mdl-27983583

RESUMO

Conventional resources of phosphorous are at high risk of depletion in the near future due to current practices of its exploitation, thus new and improved exploration methodologies need to be developed to ensure phosphorous security. Today, some treatment plants recover phosphorous from municipal wastewater as struvite (MgNH4PO4·6H2O). Magnesium is often added to the wastewater as MgCl2·6H2O to facilitate the phosphorous recovery. However, the use of magnesium increases the costs of the process and is not aligned with sustainable development, therefore, alternative magnesium sources have to be found. The current study analyzes the feasibility of integrated membrane processes for magnesium recovery from seawater for utilization in the phosphorous recovery process. The integrated membrane systems consist of nanofiltration (NF), membrane distillation (MD), and membrane crystallization (MCr). The lowest associated cost is found for standalone NF treatment. However, the additional treatment with MD and MCr produces fresh water and salts like NaCl or potentially other valuable minerals at the expense of low-grade heat.

9.
Water Sci Technol ; 73(12): 3033-40, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27332850

RESUMO

Membrane retention of the humic-like substances present in a soluble microbial products (SMP) suspension was studied by using a dead-end filtration system. The SMP suspension was extracted from the sludge of an enhanced biological phosphorus removal-membrane bioreactor. Our results showed that both adsorption and steric retention of the humic-like substances governed their transport through the membrane during the filtration. The adsorption, which followed pseudo-first order kinetics, did not cause substantial decline of permeate flux. The steric retention, on the other hand, formed a gel layer, which in turn led to a major decrease in the flux. The reduction of permeate flux was well predicted by cake filtration theory. Based on the adsorption and the steric retention, a new model was developed for predicting the overall membrane retention of the humic-like substances. The general trend of the modelled overall retention was in partial agreement with the experimental results.


Assuntos
Filtração/métodos , Substâncias Húmicas/análise , Esgotos/análise , Poluentes Químicos da Água/análise , Reatores Biológicos , Modelos Teóricos
10.
Chemphyschem ; 16(16): 3397-407, 2015 Nov 16.
Artigo em Inglês | MEDLINE | ID: mdl-26346603

RESUMO

Membrane permeability and salt rejection of a γ-alumina nanofiltration membrane were studied and modeled for different salt solutions. Salt rejection was predicted by using the Donnan-steric pore model, in which the extended Nernst-Planck equation was applied to predict ion transport through the pores. The solvent flux was modeled by using the Hagen-Poiseuille equation by introducing electroviscosity instead of bulk viscosity. γ-Alumina particles were used for ζ-potential measurements. The ζ-potential measurements show that monovalent ions did not adsorb on the γ-alumina surface, whereas divalent ions were highly adsorbed. Thus, for divalent ions, the model was modified, owing to pore shrinkage caused by ion adsorption. The ζ-potential lowered the membrane permeability, especially for membranes with a pore radius lower than 3 nm, a ζ-potential higher than 20 mV, and an ionic strength lower than 0.01 m. The rejection model showed that, for a pore radius lower than 3 nm and for solutions with ionic strengths lower than 0.01 m, there is an optimum ζ-potential for rejection, because of the concurrent effects of electromigration and convection. Hence, the model can be used as a prediction tool to optimize membrane perm-selectivity by designing a specific pore size and surface charge for application at specific ionic strengths and pH levels.

11.
Water Res ; 82: 14-24, 2015 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-25959073

RESUMO

Biological wastewater treatment removes organic materials, nitrogen, and phosphorus from wastewater using microbial biomass (activated sludge, biofilm, granules) which is separated from the liquid in a clarifier or by a membrane. Part of this biomass (excess sludge) is transported to digesters for bioenergy production and then dewatered, it is dewatered directly, often by using belt filters or decanter centrifuges before further handling, or it is dewatered by sludge mineralization beds. Sludge is generally difficult to dewater, but great variations in dewaterability are observed for sludges from different wastewater treatment plants as a consequence of differences in plant design and physical-chemical factors. This review gives an overview of key parameters affecting sludge dewatering, i.e. filtration and consolidation. The best dewaterability is observed for activated sludge that contains strong, compact flocs without single cells and dissolved extracellular polymeric substances. Polyvalent ions such as calcium ions improve floc strength and dewaterability, whereas sodium ions (e.g. from road salt, sea water intrusion, and industry) reduce dewaterability because flocs disintegrate at high conductivity. Dewaterability dramatically decreases at high pH due to floc disintegration. Storage under anaerobic conditions lowers dewaterability. High shear levels destroy the flocs and reduce dewaterability. Thus, pumping and mixing should be gentle and in pipes without sharp bends.


Assuntos
Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Filtração , Floculação , Água/química
12.
Chemosphere ; 117: 144-50, 2014 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-25014564

RESUMO

Fouling by free extracellular polymeric substances was studied in an enhanced biological phosphorus removal-membrane bioreactor. It was demonstrated that the free extracellular polymeric substances, primarily consisting of humic-like substances, were adsorbed to the membrane used in the enhanced biological phosphorus removal-membrane bioreactor plant. Infrared analyses indicated the presence of the humic-like substances on the membrane's active surface after filtration of the free extracellular polymeric substances suspension. Scanning electron microscopy showed the presence of a gel layer on the membrane surface after filtration of the free extracellular polymeric substances suspension. The gel layer caused a significant decline in water flux. This layer was not entirely removed by a backwashing, and the membrane's water flux could not be re-established. The membrane used in the enhanced biological phosphorus removal-membrane bioreactor plant showed infrared spectra similar to that fouled by the free extracellular polymeric substances suspension in the laboratory. Thus, the results of this study show the importance of humic-like substances in irreversible fouling of enhanced biological phosphorus removal-membrane bioreactor systems.


Assuntos
Reatores Biológicos , Géis/análise , Substâncias Húmicas/análise , Polímeros/metabolismo , Eliminação de Resíduos Líquidos , Adsorção , Permeabilidade , Fósforo/metabolismo
13.
Water Res ; 46(16): 4999-5008, 2012 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-22819870

RESUMO

A drainage/filtration apparatus was developed for automatically determining sedimentation velocity and dewatering rate. Pressure-step testing was used to study filter cake compressibility, resistance, and swelling. Activated sludge was analysed, and the data indicate that the sludge is highly compressible even at low pressures (10 kPa). Furthermore, compressed sludge cakes swell if the pressure is released. Hence, the average specific cake resistance decreases if the pressure is released, though the resistance is higher after the compression cycle than before. Sludge must be dewatered under low pressure, because higher pressure only compresses the cake and does not improve the dewatering rate.


Assuntos
Dessecação/métodos , Filtração/métodos , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Filtração/instrumentação , Fluoresceína , Pressão , Vácuo , Eliminação de Resíduos Líquidos/instrumentação , Água/química
14.
Water Res ; 45(19): 6453-60, 2011 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-22000719

RESUMO

Sludge-drying reed beds can be a cost-effective and sustainable solution to surplus activated sludge dewatering and mineralization, especially for small wastewater treatment plants. However, the simplicity as well as low energy and monitoring requirements of this technology are often counterbalanced by frequent operational problems consisting of slow and insufficient dewatering, poor vegetation growth, odor, and overall poor mineralization of the sludge residues. The main reason is that the general rules for facility design and operation are based on empirical experience rather than on the actual and current sludge parameters. In this study a new method for the assessment of activated sludge drainage properties has been applied to determine the reasons behind operational problems faced by the operators of reed bed facility accepting surplus activated sludge from two wastewater treatment plants in Esbjerg, Denmark. The importance of sludge quality monitoring as well as the damaging effect of shear forces, oxygen depletion, and long-distance sludge transportation were demonstrated. Finally, more general guidelines for reed bed facility design and operation are given, based on experimental data from seven full-scale plants.


Assuntos
Drenagem Sanitária , Poaceae/química , Esgotos/química , Purificação da Água/instrumentação , Purificação da Água/métodos , Simulação por Computador , Coleta de Dados , Dinamarca , Geografia , Oxigênio/análise , Fatores de Tempo , Eliminação de Resíduos Líquidos
15.
J Colloid Interface Sci ; 356(2): 681-9, 2011 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-21310425

RESUMO

Flocculation is an important process in separation science, but only few methods are available for on-line evaluation of the process. Recently, it has been shown that dielectric spectroscopy can be used to characterise the flocculation process of hard polystyrene particles. As many "real life" suspensions contain particles covered with a porous layer of organic material, it is of interest to investigate the potential of dielectric spectroscopy to characterise the flocculation of such suspensions as well. In this paper dielectric spectroscopy is used to investigate the flocculation process of core-shell particles. The flocculation process is characterised using a photometric dispersion analyser as a reference method, and the results are compared to the dielectric dispersions measured by dielectric spectroscopy. It is found that the use of the relaxation time of the dielectric dispersion for an evaluation of the flocculation process is commensurate with the use of the photometric dispersion analyser. Furthermore, the magnitude of the dielectric dispersion is observed to decrease as the charge of the core-shell particles is neutralised. Dielectric spectroscopy is thus found to have potential as an on-line flocculation monitor.

16.
Water Sci Technol ; 61(12): 3162-8, 2010.
Artigo em Inglês | MEDLINE | ID: mdl-20555213

RESUMO

A mathematical model for belt filters was developed to determine optimum load rate and belt speed during drainage of flocculated biological sludge. Numerical simulations were performed for belt filters with and without plows, and the model fit experimental data well. Experiments showed that highly compressible cakes were formed during drainage, which was important. Due to cake compression, the final sludge dry matter content increased with load rates as long as the drainage time was sufficiently long. The dry matter content could be increased by stacking the cake at the end of the process. An optimum load rate was found. At high load rates, the drainage time was too short and the dry matter content decreased with load due to high cake resistance. The resistance could be lowered by mixing cake and suspension during the process.


Assuntos
Filtração/métodos , Esgotos , Purificação da Água/métodos , Drenagem/instrumentação , Drenagem/métodos , Desenho de Equipamento , Filtração/instrumentação , Floculação , Cinética , Purificação da Água/instrumentação
17.
Water Res ; 43(3): 773-83, 2009 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-19081594

RESUMO

Pig production is concentrated in large farms, increasing the need to export excess nutrients, so manure separation would be useful to concentrate the nutrients. We examined the physicochemical properties of pig manure pertinent to flocculation and separation. Manures from three farms were stored for 3 months at 13 degrees C. The organic pools in the manure did not vary significantly during storage, so microbial metabolism was low and storage was of minor importance to separation. The manure contained highly charged particles and surface charges did not vary between the manures. This implies that the polymer doses required for flocculation can be determined directly from the manure dry matter content and that highly charged, high-molecular-weight cationic polymers can be used. Phosphorus was mainly found in the particulate fraction as struvite and was retained in the solids fraction at high pH. Thus, pH adjustment can control the amount of dissolved phosphorus in manure.


Assuntos
Esterco/análise , Sus scrofa , Animais , Tampões (Química) , Cálcio/análise , Coloides , Ácidos Graxos Voláteis/análise , Floculação , Ferro/análise , Magnésio/análise , Compostos de Magnésio/química , Esterco/microbiologia , Nitrogênio/análise , Compostos Orgânicos , Fosfatos/análise , Fosfatos/química , Potenciometria , Compostos de Amônio Quaternário/análise , Estruvita , Propriedades de Superfície
18.
Bioresour Technol ; 99(18): 8598-604, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-18474422

RESUMO

The effects of polymer flocculation before manure separation were investigated, through testing both a linear and a branched polymer. Centrifugation removed 60% of phosphorus from raw manure (control), whereas raw manure clogged the filters during gravity drainage and pressure filtration. At optimum flocculation, 95% of phosphorus was removed using any of the three methods. Optimum flocculation was achieved when 2.8meq of polymer charge was added per kg of manure, corresponding to 0.6g/kg of highly charged, branched polymer or 0.85g/kg of less-charged, linear polymer. If 10mmol of ferric chloride was added per kg of manure, 2% more phosphorus was precipitated and removed. The linear polymer formed loose flocs and was superior for reducing turbidity, whereas the branched polymer formed compact flocs that deflocculated at high polymer doses. The branched polymer, however, was best for pressure filtration, as overdosing with the linear polymer resulted in high resistance.


Assuntos
Química Orgânica/métodos , Esterco , Animais , Precipitação Química , Filtração , Floculação , Nefelometria e Turbidimetria , Fósforo/análise , Polímeros/química , Suínos
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