Low temperature Moving Bed Bioreactor denitrification as mitigation measure to reduce agricultural nitrate losses.

The negative impact of agriculture on the quality of local water streams is widely recognized. Fertilizer residues not taken up by the crops leach into the drainage water and enter the surface water, resulting in eutrophication. Despite various initiatives to prevent this leaching by optimizing fertilizer schemes, the desired effect was not achieved, and the focus has shifted to denitrifying end-of-pipe techniques. Because the available area for installing such treatment systems is often limited, the development of intensified systems is a trend that has emerged recently. In this scope, the main goal of this study was therefore to investigate the suitability of a denitrifying Moving Bed Bioreactor (MBBR) as a low footprint technology, which can compete with conventional technologies. Two parallel lab-scale pilot MBBRs, one at low temperature and one at ambient temperature, were operated for 850 days to investigate the effectiveness and robustness under changing process parameters (hydraulic retention time (HRT), temperature, shutdown). Eventually, the system was scaled up to a full-scale installation and monitored during a full drainage season in the field. The pilot-scale MBBRs achieved removal efficiencies above 90% under optimal conditions (high C/N ratio and minimal HRT of 8 h), even while operating at low temperatures. The robustness of the system was also demonstrated by the immediate start-up after a shutdown period of 220 days. Overall, the full-scale MBBR treated 2910.1 m3 drainage water and removed approximately 59 kg NO3-N. Unfortunately, the average removal efficiency, i.e., 70%, was lower than the lab-scale system, but by intensifying the mixing in the MBBR, improved results were obtained. Nitrite accumulation was furthermore also prevented.

Pilot-scale evaluation of ozone as a polishing step for the removal of nonylphenol from tank truck cleaning wastewater.

The presence of nonylphenol (NP) in the wastewater of the tank truck cleaning industry is a major concern because of its endocrine disruptive properties. In this paper, the use of ozone for degrading NP from tank truck cleaning wastewater was investigated by operating a pilot-scale biological wastewater treatment in combination with an ozonation unit. The impact of the added ozonation step on the removal of NP, soluble chemical oxygen demand (sCOD) and total organic carbon (TOC) was monitored over one year. sCOD and TOC removal were not significantly enhanced, but the NP peak concentrations in the effluent were significantly lower than those obtained after biological treatment only: a relatively low NP concentration was observed, even when peak loads were present in the influent of the pilot-scale biological wastewater treatment plant (influentbio). Contrariwise, the effluent of the sole biological treatment follows the peak load trends of the influentbio. During the ozonation period, the average NP concentration in the combined biological-ozone unit was 0.29 µg/L, compared to 1.89 µg/L for the effluent obtained after a sole biological treatment, resulting in an improved average removal efficiency of 32%.

Adsorption of phosphate on iron-coated sand granules as a robust end-of-pipe purification strategy in the horticulture sector.

Nutrient enrichment in water bodies, and its detrimental consequences, are a well known and worldwide environmental problem. Agricultural activities are identified as an important source of diffuse losses of phosphate and nitrate because of the leaching out fertilizers from agricultural fields. This study encompasses the implementation of an end-of-pipe treatment by capturing phosphate from greenhouse effluent, using granular iron-coated sand (ICS) in an adsorption process. ICS is evaluated as a low-cost by-product because of its adsorption capacity and kinetics. The Langmuir isotherm was suitable for describing the adsorption thermodynamics. The adsorption capacity at an equilibrium concentration Ce of 25 mg PO4-P/L ranged between 1.85 and 3.07 mg PO4-P/g sorbent. Furthermore, both the pseudo-second-order model (R2 = 0.9823) and the Elovich model (R2 = 0.9803) showed a good fit with the kinetic data over the time range investigated, indicating that chemisorption is the rate-limiting step controlling the adsorption process. Higher adsorption capacities were observed at lower initial pH. Continuous bench-scale column experiments were performed to verify the adsorption potential of a filter bed under flow-through conditions, and the experimental data were fit to the Bohart-Adams model. Additionally, a discontinuous feeding regime of the column, resulting in intermediate resting periods, was introduced and showed an enhanced adsorption efficiency over a longer period. Finally, a pilot-scale experiment showed the potential of the ICS for the removal of phosphate from greenhouse effluent. The adsorption process, moreover, enables the recovery of phosphate via efficient desorption.

Evaluation of process parameters of ultrasonic treatment of bacterial suspensions in a pilot scale water disinfection system.

In this study, several process parameters that may contribute to the efficiency of ultrasound disinfection are examined on a pilot scale water disinfection system that mimics realistic circumstances as encountered in an industrial environment. The main parameters of sonication are: (i) power; (ii) duration of treatment; (iii) volume of the treated sample. The specific energy (E(s)) is an indicator of the intensity of the ultrasound treatment because it incorporates the transferred power, the duration of sonication and the treated volume. In this study, the importance of this parameter for the disinfection efficiency was assessed through changes in volume of treated water, water flow rate and electrical power of the ultrasonic reactor. In addition, the influences of the initial bacterial concentration on the disinfection efficiency were examined. The disinfection efficiency of the ultrasonic technique was scored on a homogenous and on a mixed bacterial culture suspended in water with two different types of ultrasonic reactors (Telsonic and Bandelin). This study demonstrates that specific energy, treatment time of water with ultrasound and number of passages through the ultrasonic reactor are crucial influential parameters of ultrasonic disinfection of contaminated water in a pilot scale water disinfection system. The promising results obtained in this study on a pilot scale water disinfection system indicate the possible application of ultrasound technology to reduce bacterial contamination in recirculating process water to an acceptable low level. However, the energy demand of the ultrasound equipment is rather high and therefore it may be advantageous to apply ultrasound in combination with another treatment.

Evaluation of power ultrasound for disinfection of both Legionella pneumophila and its environmental host Acanthamoeba castellanii.

The objectives of this study were to (1) examine the effect of power ultrasound on the viability of both Legionella pneumophila and Acanthamoeba castellanii trophozoites and cysts, (2) investigate if intracellular Legionella replication in trophozoites positively affects bacterial resistance to ultrasound and (3) study if Legionella renders viable but non-culturable (VBNC) due to ultrasound treatments. Using laboratory scale experiments, microorganisms were exposed for various time periods to power ultrasound at a frequency of 36 kHz and an ultrasound power setting of 50 and 100%. Due to a fast destruction, trophozoite hosts were not able to protect intracellular Legionella from eradication by ultrasound, in contrast to cysts. No significant effects of ultrasound on cyst viability could be detected and power settings of 100% for 30 min only made intracellular Legionella concentrations decrease with 1.3 log units. Due to intracellular replication of Legionella in trophozoites, ultrasound no longer affected bacterial viability. Concerning the VBNC state, ultrasound treatments using a power setting of 50% partly induced Legionella (+/-7%) to transform into VBNC bacteria, in contrast to power settings of 100%. Promising results obtained in this study indicate the possible application of power ultrasound in the control of both Legionella and Acanthamoeba concentrations in anthropogenic water systems.