E. Paul

Effect of Ozonation on Activated Sludge Solubilization and Mineralization

Abstract New strategies for sludge stabilization and mineralization need to be developed since the use of sludge in agriculture is debatable and sludge incineration cannot be a systematic solution. Minimization of sludge production should be preferred. In this work, the effect of ozone on activated sludge solubilization and mineralization during batch experiments is assessed by establishing carbon and ozone mass balances. After extended ozonation of the sludge, more than 90% of the particulate carbon is modified. Depending on the experimental conditions, from 15 to 50% is found in a soluble form and from 35% to 95% was mineralized. The VSS/SS ratio decreases from 86% to less than 50% illustrating the sludge mineralization. The initial rate of ozone consumption by the sludge is very high (estimated value: 30 mgO3/g VSS.min) and corresponds to high rates of carbon solubilization and mineralization. More than 50% of the carbon obtained after ozonation is found to be readily biodegradable using a short-term BOD procedure.

Study of Competition for Ozone Between Soluble and Particulate Matter During Activated Sludge Ozonation

The use of ozone to attack soluble or solid recalcitrant compounds is often necessary to comply with environmental standards. In order to optimize ozone dosage its action must be properly targeted. Competition for ozone between soluble compounds and solid particles was studied using off-gas ozone concentration profiles. Deduced gas absorption enhancement for each matter type, alone and mixed, indicated non-classical competition. Results can be explained by the mass transfer film concept in the presence of reactive particles. Besides classical influential parameters (concentration and reactivity towards ozone), the temporary size distribution of solid particles related to the thickness of the effective liquid film must be considered.

Effect of the S0/X0 ratio on energy uncoupling in substrate-sufficient batch culture of activated sludge

Abstract A batch culture of microorganisms can be classified to substrate-limited and substrate-sufficient growth according to the initial ratio of substrate to biomass, i.e. the S 0 / X 0 ratio. It is generally observed that the excess substrate should cause serious uncoupling between anabolism and catabolism leading to energy spilling. However, how to quantitatively describe such energy uncoupling still stays unanswered for substrate-sufficient batch culture of activated sludge. Based on the observed growth yield, a concept of energy uncoupling coefficient is postulated, from which a model is proposed to describe the dependence of the energy uncoupling degree on the S 0 / X 0 ratio for substrate-sufficient batch culture. The energy uncoupling shows an increasing trend with the S 0 / X 0 ratio up to its maximum. The proposed model describes both experimental and literature data satisfactorily.

Simultaneous removal of N and P in a SBR with production of valuable compounds: application to concentrated wastewaters.

This article examines the optimisation of recovery of phosphorus and nitrogen (via struvite) in small treatment units for high strength wastewaters using biologically assisted precipitation. The particular focus was the synergetic effect between removal of orthophosphate and the biological reactions occurring during nitrogen removal. The most sensitive parameter influencing the phosphate solid forms (HAP, MAP) is pH. Sequencing batch mode helps maintain high gradients in ammonia concentration, which encourages struvite precipitation. Nitrification has a key effect on the precipitation, through its influence on pH and ammonia concentration, determining the remaining soluble phosphorus concentration. Denitrification and CO(2) stripping, by increasing pH also improve precipitation of phosphorus. Optimal operating conditions will therefore depend on the chosen strategy: thus nitrification may help to keep phosphorus in a soluble form (as needed in direct urine reuse), whereas if co-precipitation is desired in the biological reactor, nitrification should be controlled in relation with others processes responsible for pH increase.

Influence of the nature of hydrodynamic constraints on aerobic biofilms

The aim of this paper is to relate biofilm detachment to local hydrodynamics. Biofilm was submitted to erosion tests in three devices: a Couette Taylor Reactor (CTR) and two Stirred Reactors (SR) Without Baffles (WOB) and With Baffles (WB). Each device involved different hydrodynamics and different impacts on the biofilm detachment. In CTR, the detachment was significant in one specific zone on the biofilm. In SR WOB, poor detachment was observed. In SR WB, major detachment was observed only on the external face. Baffles in SR induced a transient flow and a temporal non-uniformity of shear stress improving biofilm detachment.

Influência do tipo de material suporte no desempenho de reatores biológicos de leito móvel na remoção de carbono e nitrificação de esgoto sanitário

This paper presented the influence of material support kind: P4 (rugous recycled plastic, medium diameter of 2.31 mm, density of 900 kg.m-3, specific surface potential of 2,596 m2.m-3sup) and P5 (polietilene, cilindric shape, medium diameter of 10 mm, density of 880 kg.m-3, specific surface potential of 3,075m2.m-3sup) used in two continuous flux biological moving bed reactors using different material support to remove nitrogen and carbon from sewage, which was divided in two phases according to sludge retention time (SRT): phase A: SRT of 10 days and phase B: SRT of 3 days. The organic loading rates applied were 4.0 kgCOD.m-2.d-1 (P4) and 4.1 kgCOD.m-2.d-1 (P5); and the nitrogen loading rates applied were 0.63 kgN.m-2.d-1 and 0.66 kgN.m-2.d-1 for P4 and P5, respectively. The support P4 achieved efficiencies of 87% for total carbon removal and 83% for nitrogen removal during phase A. These efficiencies slightly decreased to 80 and 77% for total carbon and nitrogen, respectively (phase B). The support P5 got removal efficiencies of 63% for total carbon and 55% for nitrogen (phase A) and 59% for total carbon and nitrogen (phase B). These results showed that the total carbon and nitrogen removal efficiencies were not affected by the SRT, but by the kind of support used (carrier geometry or surface characteristics) and available specific surface area for biomass growth.