P. Battistoni

Phosphate removal in anaerobic liquors by struvite crystallization without addition of chemicals. Preliminary results.

Abstract The feasibility of phosphate removal from the supernatant of anaerobically digested sludge by struvite (MAP, MgNH 4 PO 4 ) crystallization in a fluidized-bed reactor (FBR) was studied. Quartz sand was used as seed material. Three successive steps were investigated to highlight the process: 1, natural aging of the supernatant, with phosphate concentrations in the range 18–164 mg/l, which gave good crystallization of struvite within 3 days; 2, the inhibiting effect of Mg and bicarbonate ions on hydroxyapatite (HAP, Ca 5 OH(PO 4 ) 3 ) formation, which leads to struvite formation under supersaturation conditions; and 3, phosphate removal via the process of complete crystallization on the seed material, and which is obtained by means of external continuous aeration. All runs were performed without the addition of chemicals.

Heavy metal shock load in activated sludge uptake and toxic effects

Abstract Waste sludge from laboratory units at four different steady-state conditions (5–20 days sludge ages) was employed for studying heavy metal shock load by the jar test system. Metal uptake (Hg, Cd, Ni) and oxygen depletion rates were simultaneously followed. The potential adsorption constants ( k am ) measured reveal a metal affinity sequence Hg > Cd > Ni, in partial contrast to the metal toxicity (MT) one, Hg > Ni > Cd. This suggests different sludge adsorption sites. Hg is preferentially adsorbed on the cell, while Cd is adsorbed on extracellular polymer slimes and Ni on capsular polymers and the cellular wall. Therefore sludge age influences Cd and Ni toxicity, while no effect is observed for Hg.

Phosphorus removal from a real anaerobic supernatant by struvite crystallization

In this paper the phosphorus removal from a real anaerobic supernatant through the crystallization of struvite and or hydroxyapatite was investigated. A comparison between experimental results on phosphorus crystallization carried out in a fluidized-bed reactor (FBR) on a bench-scale and on a half-scale plant is presented, together with a double saturational model able to describe all experimental results, independent of the different geometry of the reactors, the distinct contact times and the unlike products obtained. Experimental results show that removal efficiencies are very satisfactory, and the maximum phosphorus removal is of 80%.

P removal from anaerobic supernatants by struvite crystallization: long term validation and process modelling

In this work, a model for phosphorus crystallization in a fluidized bed reactor, able to describe the experimental results obtained during a semiscale pilot plant, is presented. In particular, the validity of the model proposed has been evenly extended with respect to a previous experiment, even at a lower contact time, and the length of each experiment has been increased, in order to verify the behaviour of the process for long term applications and to evaluate the maximum crystal growth of the system. Moreover, the state of the art of the available processes for phosphorus removal from wastewater is presented, together with a detailed review of the several models so far developed to describe the phosphorus crystallization mechanisms.

Excess sludge reduction by biological way: from experimental experience to a real full scale application.

The aim of this study was to investigate the ability of a biological process applied in the sludge line and based on the alternation of oxic and anoxic phases, to minimize the waste sludge production. After some tests in pilot scale, the process was applied in a real municipal wastewater treatment plant of 35,000 PE trying out one setting of working experimental conditions. A rate of the recycle flow was conditioned in a treatment basin, maintaining an HRT of 10 days. The control device operated for the 50% of time in the ORP range between -400 and -200 mV, and for the 50% in the ORP range between -200 and +50 mV. The mass balance defined an actual observed growth yield equal to 0.09 kgTVSkgCODr(-1), and the heterotrophic yield values, assessed by batch tests, seemed to be a suitable marker for the sludge reduction and for the energy uncoupling.

The under sink garbage grinder: A friendly technology for the environment

Abstract The use of garbage grinders is not a usual practice in Europe, but it is in other countries around the world (e.g., North America, Japan and Australia). Sometimes, garbage grinders are accused of producing problems in sewers and wastewater treatment plants and are prohibited by environmental protection laws. In this study, the different impacts determined by the use of this technology were considered to show the positive impacts of its use. In particular, it was shown that garbage grinders enable the disposal of household organic wastes with advantages for the wastewater treatment processes because of an increase in the carbon/nutrients ratio in the wastewater. This is particularly important for biological nutrients removal processes. Daily specific contributions for person equivalent (PE) due to organic waste disposal through garbage grinders were found to be equal to 75 gCODPE−1d−1 for carbon (as COD), 2.5 gNPE−1d−1 for nitrogen and 0.25 gPPE−1d−1 for phosphorous, respectively. Those determined a value of 30 for the COD/N ratio. Moreover, no problems with solids settling in sewers were noted. These results were extensively compared with literature data. The economical balance showed that the use of garbage grinders allowed a global saving of some 17 €year−1 for a three people family. Important benefits are also gained from an environmental point of view (e.g., organic wastes disposal, nutrients removal in wastewater treatment and increase in biogas production with energy reclamation)

Auto-nucleation and crystal growth of struvite in a demonstrative fluidized bed reactor (FBR)

The experience of P removal by auto nucleation and crystal growth of struvite (MAP) in a demonstrative plant is proposed. The demonstrative plant is located in a municipal wastewater treatment plant in northern Italy. The trials are a consequence of previous experimentation carried out using silica sand as seed material. Working in metastable conditions the auto-nucleation process is performed, and allows the control of the precipitation and the growth of MAP inside the FBR reactor. No scaling problems are observed in the collecting pipes. After the treatment of 650m3 of anaerobic supernatants, 0.28 tons of granulated crystalline MAP are produced. The chemical analysis shows its possible use in agriculture as fertilizer. Operative costs analysis confirms the SCP as a cheap way to remove and recover P from anaerobic supernatants.

Exploring the potential of membrane bioreactors to enhance metals removal from wastewater : pilot experiences

The potential of membrane bioreactors to enhance the removal of selected metals from low loaded sewages has been explored. A 1400 litre pilot plant, equipped with an industrial submerged module of hollow fibre membranes, has been used in three different configurations: membrane bioreactor, operating in sequencing batch modality, for the treatment of real mixed municipal/industrial wastewater; membrane-assisted biosorption reactor, for the treatment of real leachate from municipal landfills; continuously fed membrane bioreactor, for the treatment of water charged with cadmium and nickel ions. The results show that: (a) in treating wastewaters with low levels of heavy metals (< one milligram per litre concentration), operating high sludge ages is not an effective strategy to significantly enhance the metals removal; (b) Hg and Cd are effectively removed already in conventional systems with gravitational final clarifiers, while Cu, Cr, Ni can rely on a additional performance in membrane bioreactors; (c) the further membrane effect is remarkable for Cu and Cr, while it is less significant for Ni. Basically, similar membrane effects recur in three different experimental applications that let us estimate the potential of membrane system to retain selected metal complexes. The future development of the research will investigate the relations between the membrane effect and the manipulable filtration parameters (i.e., permeate flux, solids content, filtration cycle).

Switching small WWTPs from extended to intermittent aeration: process behaviour and performances

The paper presents the one year results obtained by a small wastewater treatment plant (WWTP) located in a decentralized area. The plant was organized, reusing current structures, introducing an equalization tank, an anoxic selector and the alternate cycles (AC) as technology in the biological process. The experimentation data processed show the excellent quality of the effluent with high removal efficencies for all the macropollutants. Also, the anoxic selector effect allows, in the critical winter period, the decrease in the filamentous bacteria total number, a net improvement of the settling behaviour with an average solid maximum flux value of 3.8 kgMLSSm(-2) h(-1) and a good mixed liquor settleability. The alternate cycles process flexibility consents to well manage the high fluctuations of the influent loadings. The costs comparison of AC process and extended aeration confirms the sustainability of the upgrading.

Rheology of sludge from semi-dry anaerobic digestion of municipal solid waste

Abstract Rheology of anaerobically digested organic fractions of municipal solid waste was studied. A wide range of total solids content (4–33%) in sludges from a plant operating at mesophilic and thermophilic conditions were examined. The rheological behaviour was described adopting a plastic model. High fluidity and low thixotropy for a content up to 10–12% of total volatile solids and an exponential correlation between rigidity coefficient or yield stress and total volatile solids were found. Significant correlations were found between rheological parameters and sludge properties or process performance.