Erik B. Muller

Aerobic domestic waste water treatment in a pilot plant with complete sludge retention by cross-flow filtration

Abstract An aerobic wastewater treatment pilot plant with cross-flow filtration was operated for more than 300 days to examine whether reduced sludge production and stable treatment performance can be achieved when sludge is completely retained. The volumetric loads ranged between 0.9 and 2.0 g COD·1 −1 ·day −1 . Technical observations were: the oxygen transfer rate became poor at high sludge concentrations; membrane capacities declined but could be mostly sufficiently restored by cleaning. Sludge was hardly produced when the mixed liquor suspended solid (MLSS) concentration had increased to 40–50 g·1 −1 . Then, the sludge load was only 0.021 g CD·g MLSS −1 ·day −1 and only 6% of the carbon supplied was assimilated. Non-volatile compounds hardly accumulated as the fraction of inorganic compounds in sludge increased from 21.6 to 23.5% during the last 200 days, whereas the carbon, phosphor and kjeldahl nitrogen contents were stable. After 300 days the content of polluting trace elements, such as mercury, lead and cadmium, were similar to that of a conventional treatment plant supplied with this wastewater. Carbon and kjeldahl nitrogen removal was always quite satisfactory. Carbon was always removed for more than 90% and kjeldahl nitrogen that was not assimilated was completely nitrified at all times. The nitrification capacity at 30°C was constantly around 0.2 mmol·g MLSS −1 ·h −1 , which shows that the viability of the nitrifying population did not cease. In addition, up to 40% of nitrogen supplied was lost as a result of denitrification. Hence stable treatment performance and a very low sludge production can be achieved when complete sludge retention is applied at high hydraulic loads.

Impacts of Metal Oxide Nanoparticles on Marine Phytoplankton

Information on the toxicity of environmentally relevant concentrations of nanoparticles in marine ecosystems is needed for informed regulation of these emerging materials. We tested the effects of two types of metal oxide nanoparticles, TiO(2) and ZnO, on population growth rates of four species of marine phytoplankton representing three major coastal groups (diatoms, chlorophytes, and prymnesiophytes). These metal oxide nanoparticles (NPs) are becoming common components in many industrial, household, and cosmetic products that are released into coastal ecosystems. Titania NPs showed no measurable effect on growth rates of any species, while ZnO NPs significantly depressed growth rate of all four species. ZnO NPs aggregated rapidly in seawater, forming particles >400 nm hydrodynamic diameter within 30 min, and dissolved quickly, reaching equilibrium concentrations within 12 h. Toxicity of ZnO NPs to phytoplankton was likely due to dissolution, release, and uptake of free zinc ions, but specific nanoparticulate effects may be difficult to disentangle from effects due to free zinc ions. A modeling approach based on a Dynamic Energy Budget (DEB) framework was used to estimate sublethal effects of the two NPs on phytoplankton populations. Concentrations that were estimated to have no effect on population growth (NEC) were (one standard error in parentheses) 428 (58) μg L(-1) ZnO for the diatom Skeletonema marinoi and 223 (56) μg L(-1) for Thalassiosira pseudonana. NEC could not be estimated for the other taxa but were within the range of 500-1000 μg L(-1). Our results suggest that effects of metal oxide NPs on marine organisms is likely to vary with particle type and organism taxonomy.

Bullfrogs, disturbance regimes, and the persistence of California red-legged frogs

The introduction and spread of bullfrogs (Rana catesbeiana) in western North America may have played a central role in the declines of native ranid frogs. Specifically, a positive corielation exists between the absence of California red-legged frogs (Rana aurora draytonii) and the presence of introduced bullfrogs, but coexistence does occur in some environments. Enclosure experiments and diet studies have shown that bullfrogs prey on larval and juvenile California red-legged frogs. We used a modeling approach to quantify the threat of bullfrog predation on California red-legged frog populations. We created age-structured population models for both species. We used these models to (I) explore the sensitivity of red-legged frog populations to changes in the intensity of bullfrog predation; (2) explore the hypothesis that high flood frequencies increase the probability for coexistence in southern California streams; and (3) examine the efficacy of bullfrog management strategies, such as shooting adults and draining livestock grazing ponds. Our model simulations indicated that winter floods, which strongly increase mortality of bullfrogs but not red-legged frogs, facilitate coexistence if they occur more than once every 5 years. We found that increasing adult bullfrog mortality through shooting would benefit red-legged frogs only with extreme effort. Conversely, the draining of livestock grazing ponds can be effective in bullfrog management if claiming occurs at least every 2 years. Shooting and draining in tandem were successful at decreasing bullfrog densities. Finally, our model provided a quantitative measure of bullfrog predation on California red-legged frogs that can potentially be used to assess the impact of bullfrogs on a site-by-site basis. Our model plus experimental studies that link specific environmental factors to the bullfrog predation rate, can provide managers with a useful tool for controlling populations and facilitating conservation efforts for the California red-legged frog.

Dynamic energy budgets in syntrophic symbiotic relationships between heterotrophic hosts and photoautotrophic symbionts.

In this paper we develop and investigate a dynamic energy budget (DEB) model describing the syntrophic symbiotic relationship between a heterotrophic host and an internal photoautotrophic symbiont. The model specifies the flows of matter and energy among host, symbiont and environment with minimal complexity and uses the concept of synthesizing units to describe smoothly the assimilation of multiple limiting factors, in particular inorganic carbon and nitrogen, and irradiance. The model has two passive regulation mechanisms: the symbiont shares only photosynthate that it cannot use itself, and the host delivers only excess nutrients to the symbiont. With parameter values plausible for scleractinian corals, we show that these two regulation mechanisms suffice to obtain a stable symbiotic relationship under constant ambient conditions, provided those conditions support sustenance of host and symbiont. Furthermore, the symbiont density in the host varies relatively little as a function of ambient food density, inorganic nitrogen and irradiance. This symbiont density tends to increase with light deprivation or nitrogen enrichment, either directly or via food. We also investigate the relative benefit each partner derives from the relationship and conclude that this relationship may shift from mutualism to parasitism as environmental conditions change.

Impact of Engineered Zinc Oxide Nanoparticles on the Individual Performance of Mytilus galloprovincialis

The increased use of engineered nanoparticles (ENPs) in consumer products raises the concern of environmental release and subsequent impacts in natural communities. We tested for physiological and demographic impacts of ZnO, a prevalent metal oxide ENP, on the mussel Mytilus galloprovincialis. We exposed mussels of two size classes, <4.5 and ≥4.5 cm shell length, to 0.1–2 mg l−1 ZnO ENPs in seawater for 12 wk, and measured the effect on mussel respiration, accumulation of Zn, growth, and survival. After 12 wk of exposure to ZnO ENPs, respiration rates of mussels increased with ZnO concentration. Mussels had up to three fold more Zn in tissues than control groups after 12 wk of exposure, but patterns of Zn accumulation varied with mussel size and Zn concentrations. Small mussels accumulated Zn 10 times faster than large mussels at 0.5 mg l−1, while large mussels accumulated Zn four times faster than small mussels at 2 mg l−1. Mussels exposed to 2 mg l−1 ZnO grew 40% less than mussels in our control group for both size classes. Survival significantly decreased only in groups exposed to the highest ZnO concentration (2 mg l−1) and was lower for small mussels than large. Our results indicate that ZnO ENPs are toxic to mussels but at levels unlikely to be reached in natural marine waters.

Simultaneous NH3 oxidation and N2 production at reduced O2 tensions by sewage sludge subcultured with chemolithotrophic medium

The ammonia oxidation rate by sewage sludge was determined as a function of the dissolved oxygen tension. Samples of sludge were taken from a domestic waste water treatment pilot plant in which sludge was completely retained by membrane filtration. The samples were subcultured chemolithotrophically in recycling reactors. The gas supplied was a mixture of pure argon and oxygen. The KO2 for ammonia oxidation was estimated to be 0.97 (±0.16) kPa dissolved oxygen. Together with ammonia oxidation and oxygen consumption, dinitrogen gas was produced. So, aerobic denitrification occurred. At dissolved oxygen tensions of 1.25 kPa and higher, the dinitrogen production rate (per N-mole) equalled 20% of the ammonia oxidation rate. This proportion was even 58% at 0.3 kPa dissolved oxygen. At 0.15 kPa dissolved oxygen, however, nitrification hardly proceeded, while dinitrogen production soon stopped. Most likely, a nitrifier concomitantly oxidized ammonia and reduced nitrite to dinitrogen.

Microbial growth dynamics on the basis of individual budgets

The popular theories for microbial dynamics by Monod, Pirt and Droop are shown to be special cases of a model for individual budgets, in which growth and maintenance are on the expense of reserve materials. The dynamics of reserve materials is a first order process with a relaxation time proportional to cell length; maintenance is proportional to cell volume, and uptake, which depends hyperbolically on substrate density, is proportional to cell volume as well. Because of the latter, population dynamics depends on the behaviour of the individuals in a simple way, such that the cell volume distribution has no quantitative effect.

A novel method to determine maximal nitrification rates by sewage sludge at a non-inhibitory nitrite concentration applied to determine maximal rates as a function of the nitrogen load

Abstract A new method was developed to determine the maximal nitrification capacity of sewage sludge. Samples of sludge were taken from two domestic waste water treatment plants and were chemolithotrophically grown in recycling reactors. The experimental duration was typically in the order of hours. The maximal nitrification rates were estimated from the concentrations of nitrogen compounds in effluents. These rates could be easily determined by first order kinetics, since substrates were supplied in excess and growth was generally negligible. However, accumulation of nitrite affected the ammonia oxidation rates. At 3–5 mM nitrite these rates were halved as compared to 0–1 mM. Since the accumulated nitrite is continuously diluted without loss of sludge, recycling reactors are especially suitable to study nitrification. Subsequently, this method was applied to investigate the development of the maximal nitrification capacity as a function of the nitrogen load. For this purpose, sludge was subcultured with synthetic waste water in recycling reactors. Since heterotrophic ammonium assimilation was negligible, the final capacities were proportional to the nitrogen load. However, these capacities were lower than expected. Since the numbers of protozoa had increased, predation might have reduced the nitrifying population

Dynamic energy budget modeling reveals the potential of future growth and calcification for the coccolithophore Emiliania huxleyi in an acidified ocean

Ocean acidification is likely to impact the calcification potential of marine organisms. In part due to the covarying nature of the ocean carbonate system components, including pH and CO2 and CO3(2-) levels, it remains largely unclear how each of these components may affect calcification rates quantitatively. We develop a process-based bioenergetic model that explains how several components of the ocean carbonate system collectively affect growth and calcification rates in Emiliania huxleyi, which plays a major role in marine primary production and biogeochemical carbon cycling. The model predicts that under the IPCC A2 emission scenario, its growth and calcification potential will have decreased by the end of the century, although those reductions are relatively modest. We anticipate that our model will be relevant for many other marine calcifying organisms, and that it can be used to improve our understanding of the impact of climate change on marine systems.

Modeling the effect of toxicants on the parameters of dynamic energy budget models

Toxicants negatively affect the rates of growth and reproduction of organisms. Dynamic energy budget models offer a convenient mathematical framework to describe growth and reproduction by individuals. Since these models take into account the lipid content of an animal, the accumulation of toxicants is easily incorporated. This paper deals with the subsequent effects of toxicants on growth and reproduction. We argue that the concept of non-competitive inhibition is applicable for toxicants that increase maintenance demands and reduce assimilation. In this way, energy investment in growth and reproduction are indirectly reduced.