Trickling filter

About: Trickling filter is a research topic. Over the lifetime, 1098 publications have been published within this topic receiving 20219 citations.

Oxygen utilization of trickling filter biofilms

Abstract: In-situ oxygen consumption rate (OCR) observations for trickling filter biofilms under different hydraulic, substrate loading, and oxygen availability operating conditions are presented. OCRs were determined for sucrose- and dextrin-based synthetic feedstocks by growing biofilms on a 1.2-m deep section of 60° cross-flow media that was enclosed within a reactor vessel, sealing the reactor vessel to outside air entry, and observing the time rate of decrease in the reactor’s oxygen partial pressure. The results indicate that OCRs increased proportionately with increasing influent substrate concentrations for the 40 to 120 mg/L SCOD range, increased slightly or remained relatively constant with increasing influent substrate concentrations for the 120 to 200 mg/L SCOD range, increased slightly with increasing DO saturation condition for the 7.4 to 10.1 mg/L range, were affected by oxygen availability for influent substrate concentrations throughout the 70 to 175 mg/L SCOD range, increased with increasing hydraulic application rate from 2.4 to 4.9 m³/m²-h, and were slightly greater than predicted by currently acknowledged models. Other observations include the following measured OCRs were at least three times greater than those estimated from clean media oxygen-transfer testing; without liquid and feedstock application, biofilms consumed oxygen at 80–104% of their usual rate; and maximum biofilm oxygen consumption was ≈680 mg/m²-h.

Dynamics of specific ammonia-oxidizing bacterial populations and nitrification in response to controlled shifts of ammonium concentrations in wastewater

Abstract: Ammonia-oxidizing bacteria (AOB) are essential for the nitrification process in wastewater treatment. To retain these slow-growing bacteria in wastewater treatment plants (WWTPs), they are often grown as biofilms, e.g., on nitrifying trickling filters (NTFs) or on carriers in moving bed biofilm reactors (MBBRs). On NTFs, a decreasing ammonium gradient is formed because of the AOB activity, resulting in low ammonium concentrations at the bottom and reduced biomass with depth. To optimize the NTF process, different ammonium feed strategies may be designed. This, however, requires knowledge about AOB population dynamics. Using fluorescence in situ hybridization (FISH) and confocal laser scanning microscopy, we followed biomass changes during 6 months, of three AOB populations on biofilm carriers. These were immersed in aerated MBBR tanks in a pilot plant receiving full-scale wastewater. Tanks were arranged in series, forming a wastewater ammonium gradient mimicking an NTF ammonium gradient. The biomass of one of the dominating Nitrosomonas oligotropha-like populations increased after an ammonium upshift, reaching levels comparable to the high ammonium control in 28 days, whereas a Nitrosomonas europaea-like population increased relatively slowly. The MBBR results, together with competition studies in NTF systems fed with wastewater under controlled ammonium regimes, suggest a differentiation between the two N. oligotropha populations, which may be important for WWTP nitrification.

Biological Drinking Water Treatment of Anaerobic Groundwater in Trickling Filters

Abstract: Drinking water production from anaerobic groundwater is usually achieved by so called conventional techniques such as aeration and sand filtration. The notion conventional implies a long history and general acceptation of the application, but doesn’t necessarily mean a thorough understanding of the processes involved. This is certainly the case for groundwater filtration, with groundwater being the major source for drinking water production in the world. During infiltration and soil passage groundwater may become deeply anaerobic and be loaded with methane, iron, ammonium and manganese that have to be removed during drinking water production. The removal processes for these compounds may be physical-chemical or biological. Since the important PhD-researchers Lerk and Graveland used a chemical approach in the 1960th, the general perception is that only methane and ammonium removal is biological under environmental conditions. Biological iron and manganese removal would be more exceptional as a result of the specific conditions required. The origin of this PhD lies in a persistent nitrification problem in the filters of Oasen Drinking Water Company. When no strong chemical oxidizers are used, like in the Netherlands, nitrification is the only applicable process to fully remove ammonium. It comprises the two-step biological conversion of ammonia via nitrite to nitrate. The first step, the microbial oxidation of ammonia to nitrite, becomes incomplete during the aging of the filter. The relapse typically becomes visible three to six months after the startup of a filter with new filter material. Oasen has only one technique to counteract these nitrification problems, namely subsurface aeration. In that technique, a limited amount of aerated water is periodically injected into the groundwater aquifer, resulting in in situ iron oxidation. The iron colloids that are also formed in the aquifer stimulate the nitrification in the filters, but the working mechanism is unknown. As this “Wonder van Nieuw Lekkerland” is not understood and restricted by licenses, Oasen looks for alternative techniques to maintain a sound nitrification. The general hypothesis for this problem was that the nitrification problem resulted from the interaction with the other removal processes. The problem was studied in full-scale filters and lab-scale setups. Molecular techniques, such as DGGE and clone libraries, were used to identify the major groups of microorganisms present in the groundwater and filters. Ammonia oxidation is performed by Nitrosomonas and archaea, nitrite oxidation by Nitrospira, while Nitrobacter bacteria are not found in drinking water filters. Notable was the presence of the iron-oxidizing Gallionella bacteria in the subsurface aerated groundwater. Another molecular technique, quantitative PCR, was used to quantify Gallionella and ammonia-oxidizing bacteria and archaea in all incoming and outgoing water flows and attached to the filter material. From these numbers balances were made for the filters. The activity of the ammonia-oxidizers was assessed in standardized batch experiments. One of the major findings was that Gallionella grew extensively in a groundwater filter with nitrification problems. In a filter fed with subsurface aerated water, however, Gallionella pumped up with the subsurface aerated water did not continue to grow in the filter. In fact, clone libraries showed, that Gallionella growing in situ deviated from the ones growing in the filter. The growth of Gallionella in well-ventilated trickling filters is remarkable, because these organisms are supposed to be micro-aerophilic. Trickling filters are used for their efficient gas transfer, resulting in effective aeration and stripping of methane and carbon dioxide. The effluent water has a pH of 7.5 to 8 and is almost saturated with oxygen. To verify the growth of Gallionella under these conditions Gallionella bacteria were cultured in continuously operated oxidation and filtration columns (Figure 1). These experiments confirmed the growth of Gallionella under oxygen saturated conditions and at a pH up to 7.7 (Figure 2). The balance approach of ammonia-oxidizing bacteria (AOB) showed that the nitrification problem was not caused by the excessive washout of these microorganisms. In fact, the number of AOB was higher in a filter with nitrification problems, but their activity was much lower. This low cell-specific activity was caused by limitation of the essential nutrient phosphate that could be corrected by addition of phosphate (see Figure 3). So what is the relation between the growth of Gallionella and nitrification problems? While phosphate in groundwater is readily removed for the greater part by co-precipitation with chemically formed iron oxyhydroxides, the biogenic iron precipitates of Gallionella have a higher adsorption capacity for phosphate and further lower the phosphate concentration to limiting levels for the growth of AOB. The outcome of this PhD research provides solutions for the groundwater nitrification problem (such as phosphate dosage and suppression of Gallionella growth) and perspective to further optimize trickling filtration, the most efficient process to remove methane and iron from groundwater.