Sewage sludge pretreatment: current status and future prospects.

Sewage sludge is regarded by wastewater treatment plants as problematic, from a financial and managerial point of view. Thus, a variety of disposal routes are used, but the most popular is methane fermentation. The proportion of macromolecular compounds in sewage sludges varies, and substrates treated in methane fermentation provide different amounts of biogas with various quality and quantity. Depending on the equipment and financial capabilities for methane fermentation, different methods of sewage sludge pretreatment are available. This review presents the challenges associated with the recalcitrant structure of sewage sludge and the presence of process inhibitors. We also examined the diverse methods of sewage sludge pretreatment that increase methane yield. Moreover, in the field of biological sewage sludge treatment, three future study propositions are proposed: improved pretreatment of sewage sludge using biological methods, assess the changes in microbial consortia caused with pretreatment methods, and verification of microbial impact on biomass degradation.

The influence of antibiotics on the anammox process - a review.

Anaerobic ammonium oxidation (anammox) is one of the most promising processes for the treatment of ammonium-rich wastewater. It is more effective, cheaper, and more environmentally friendly than the conventional process currently in use for nitrogen removal. Unfortunately, anammox bacteria are sensitive to various substances, including heavy metals and organic matter commonly found in the wastewater treatment plants (WWTPs). Of these deleterious substances, antibiotics are recognized to be important. For decades, the increasing consumption of antibiotics has led to the increased occurrence of antibiotics in the aquatic environment, including wastewater. One of the most important issues related to antibiotic pollution is the generation and transfer of antibiotic resistance bacteria (ARB) and antibiotic resistance genes (ARGs). Here, we will discuss the effect of short- and long-term exposure of the anammox process to antibiotic pollutants; with a special focus on the activity of the anammox bacteria, biomass properties, community structures, the presence of antibiotic resistance genes and combined effect of antibiotics with other substances commonly found in wastewater. Further, the defense mechanisms according to which bacteria adapt against antibiotic stress are speculated upon. This review aims to facilitate a better understanding of the influence of antibiotics and other co-pollutants on the anammox process and to highlight future avenues of research to target gaps in the knowledge.

Medium shift influence on nitrogen removal bacteria: Ecophysiology and anammox process performance.

In this study, we focused on the proportion of particular bacterial groups and changes in microbial community structure in relation to the anammox process parameters and the feeding medium strategy in the Sequencing Batch Reactor (SBR). In order to present an insight into the microbial dynamics while feeding medium shift from synthetic wastewater to landfill leachate, fluorescent in situ hybridization (FISH), Real Time PCR, PCR - DGGE (Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis) and Reverse Transcription PCR-DGGE analysis were used. Feeding medium change has the strongest impact on relative abundance of denitrifiers and representatives of Planctomycetes. The relative abundancy of specific genes for all investigated nitrogen removal bacterial groups dropped after landfill leachate implementation. However, anammox consortium were able to adapt to the new reactor operating conditions and time for adaptation was estimated at the level of 90 days.

Bacterial community structure in rotating biological contactor treating coke wastewater in relation to medium composition.

Biological wastewater treatment using biofilm systems is an effective way to treat difficult wastewater, such as coke wastewater. The information about the structure and the dynamics of this microbial community in biofilm, which are responsible for wastewater treatment, is relevant in the context of treatment efficacy and the biochemical potential to remove various pollutants. However, physico-chemical factors can influence the biofilm community significantly, causing performance disturbances. Therefore, we decided to examine the structure of microbial community in rotating biological contactor (RBC) biofilm during coke wastewater treatment and to investigate the possible shift in the community structure caused by the feeding medium change from synthetic to real coke wastewater. The experiment performed with high-throughput next-generation sequencing (NGS) revealed that bacteria commonly present in wastewater treatment plant (WWTP) systems, responsible for nitrite oxidizing, such as Nitrospira or Nitrobacter, were absent or below detection threshold, while Nitrosomonas, responsible for ammonia oxidizing, was detected in a relatively small number especially after shift to real coke wastewater. This research indicates that medium change could cause the change from autotrophic into heterotrophic nitrification led by Acinetobacter. Moreover, biofilm systems can be also a potential source of bacteria possessing high biochemical potential for pollutants removal but less known in WWTP systems, as well as potentially pathogenic microorganisms.

Cold anammox process and reduced graphene oxide - Varieties of effects during long-term interaction.

Because of its energy efficiency, the anaerobic ammonium oxidation (anammox) process has been recognized as the most promising biological nitrogen removal process, but its implementation in mainstream wastewater treatment plants is limited by its relatively high optimal temperature (30 °C). Recently, it was shown that during short-term batch experiments, reduced graphene oxide (RGO) displayed accelerated reaction activity at low temperatures (10-15 °C). In this study, the long-term effects of RGO on the low-temperature anammox process in a sequencing batch reactor (SBR), are studied for the first time, including different methods of interaction. The results presented here show that RGO can stimulate anammox activity up to 17% through two factors: bacterial growth stimulation, which was especially significant at higher temperatures (>15 °C), and an increase of the anammox reaction rate, which occurred only below 15 °C. The bacterial community structure was not influenced by addition of RGO. Moreover, after incubation in an anammox bioreactor, RGO showed signs of degradation and chemical changes as evidenced by the presence of oxygen and calcium on its surface. According to the literature and the obtained results, it is proposed that RGO is oxidized and oxygen is reduced by the organic mediator that is involved in the enzymatic reactions. However, activated sludge is a very complex structure created by numerous, undefined microorganisms, which makes it difficult to determine the exact oxidation mechanism.

Short-term effects of reduced graphene oxide on the anammox biomass activity at low temperatures.

Anaerobic ammonium oxidation (anammox) is an efficient process for nitrogen removal from wastewater, but its common use is limited by its relatively high optimal temperature (30 °C). One of the major bottlenecks of the implementation of mainstream PN/A process is the low activity of the anammox bacteria at low temperature. Due to this reason over the past years, numerous researchers have attempted to overcome this limitation. Recently it was shown that the reduced graphene oxide (RGO) can accelerate the anammox bacteria activity. However all these studies were performed at high temperatures (over 30 °C). Thus, in this study, supporting the anammox process at low temperatures (10-30 °C) by the RGO was investigated for the first time. The statistical analysis confirmed that RGO significantly affects the anammox activity. The stimulation effect of RGO on the anammox bacteria activity is of particular importance at low temperatures, when drastic decrease in process activity is observed at temperatures below 15 °C. The short-term experimental results demonstrated stimulation of the anammox activity at 13 °C, up to 28% by 15 mg RGO/L, but concentrations above 40 mg RGO/L caused the process inhibition, up to 30% with 50 mg RGO/L. However, the effect of RGO probably depends on the nanomaterial dose per biomass unit and the optimal range of this value was evaluated as 20 to 45 mg RGO/g VSS (volatile suspended solids).

Significance of pH control in anammox process performance at low temperature.

Anaerobic ammonium oxidation (anammox) is an efficient process for biological nitrogen removal from wastewater. Common use of this technology is still limited by relatively high optimal temperature. Temperature and pH influence on the anammox process was widely studied, but the significance of pH control in the anammox performance at low temperature was omitted. Moreover up to now, these two parameters were analyzed separately without looking into the composite effects. Statistical approach was used to conduct an in-depth study of the individual and interactive influence of pH and low temperature on the anammox activity. Optimal pH was observed between 7.0 and 7.5, but results indicate that there is no statistically significant interaction between pH and temperature. However, it was observed that the optimal pH range narrows along with the temperature decrease, which means that the efficiency of the anammox process at low temperatures can be improved by correction and adequate control of pH.

Influence of temperature and pH on the anammox process: A review and meta-analysis.

The anammox (anaerobic ammonium oxidation) process was considered a very efficient and economic wastewater treatment technology immediately after its discovery in 1995, thus research in this field was intensified. The anammox process is characterised by a high temperature optimum and is very sensitive to both temperature and pH fluctuations. The process can also be inhibited by many factors, including by its substrates, i.e. nitrite and ammonium (or its unionised forms: free ammonia and free nitrous acid). This paper presents a comprehensive study of the most important and recent findings on the influence of two parameters that are crucial in wastewater treatment, i.e. temperature and pH. Because both parameters may influence the anammox process simultaneously, a meta-analysis was conducted of the data from the literature. Although meta-analysis is commonly used in medical research, mathematical analysis of the literature data has become an interesting and important step in the environmental sciences. This paper presents information on the influence of both temperature and pH on process efficiency and microbial composition. Additionally, the responses of different operating systems on both temperature and pH changes are described. Moreover, the role of both adaptation to changed conditions and of pH control as well as indicated areas of process operation are discussed.

Removal of Nitrogen and Phosphorus From Reject Water Using Chlorella vulgaris Algae After Partial Nitrification/Anammox Process.

Wastewater containing nutrients like ammonia, nitrite, nitrate and phosphates have been identified as the main cause of eutrophication in natural waters. Therefore, a suitable treatment is needed. In classical biological processes, nitrogen and phosphorus removal is expensive, especially due to the lack of biodegradable carbon, thus new methods are investigated. In this paper, the new possibility of nitrogen and phosphorus removal in side stream after the partial nitrification/Anammox process is proposed. Research was carried out in a lab-scale vertical tubular photobioreactor (VTR) fed with real reject water, from dewatering of digested sludge, after partial nitrification/Anammox process from lab-scale sequencing batch reactor (SBR). Nitrogen and phosphorus concentrations were measured every three days. The average nitrogen and phosphorus loads were 0.0503 ± 0.036 g N g(vss)/d and 0.0389 ± 0.013 g P g(vss)/d accordingly. Results have shown that microalgae were able to efficiently remove nitrogen and phosphorus. The average nitrogen removal was 36.46% and phosphorus removal efficiency varied between 93 and 100%.

R&D priorities in the field of sustainable remediation and purification of agro-industrial and municipal wastewater.

This article was presented as a position paper during the Environmental Biotechnology and Microbiology Conference in Bologna, Italy in April 2012. It indicates major and emerging environmental biotechnology research and development (R&D) priorities for EU members in the field of sustainable remediation and purification of agro-industrial and municipal wastewater. The identified priorities are: anaerobic/aerobic microbial treatment, combination of photochemical and biological treatment, phytoremediation and algae-based remediation, as well as innovative technologies currently investigated, such as enzyme-based treatment, bioelectrochemical treatment and recovery of nutrients and reuse of cleaned water. State of the art, research needs and prospective development in these domains are crucially discussed. As a result, goals of the future development of bioremediation and purification processes are defined and the way to achieve them is proposed.