Psychrophilic Digestion Research Articles

The application of psychrophilic digestion for municipal sewage treatment

The application of psychrophilic digestion for municipal sewage treatment

Emission of Biogas from Sewage Sludge in Psychrophilic Conditions

The stabilization of sewage sludge in Poland is continued in many sewage treatment plants in the open digestion chambers (ODC), which is a phenomenon on the European scale. The sludge is stored in them much longer, which allows obtaining high mineralization of the material, thanks to which it can be used naturally. Although this way of sludge processing is very beneficial owing to the high quality of the final product, the ODC are a source of gas emissions, because the biogas produced in them is usually not detracted. The research was carried out at the “Boguszowice” sewage treatment plant in Poland, which is equipped with two ODC with a capacity of 5781 m3 each. Within the chambers a process of stabilization of sludge is carried out based on psychrophilic digestion (i.e. temperature < 20 °C). The tests were carried out in two variants. In the first variant, the measurements of the flow of biogas produced were made directly on the open digestion chamber by means of a floating sampler. In the second variant, simulations of the digestion process under laboratory conditions were carried out. Analyzing the results, the high quality of the obtained biogas for both variants of the conducted research can be noticed. The average methane concentration in biogas for real tests was 68.5% and for laboratory tests 69.7%. Scheme of psychrophilic digestion.

Influence of seasonal fluctuation and loading rates on microbial and chemical indicators during semi-continuous anaerobic digestion

Minimal attention is paid towards the performance of the 40 million small-scale digesters which frequently operate at psychrophilic temperatures. Understanding the levels of microbial and chemical indicators at various loading rates and temperatures is useful for improving treatment efficiency and management strategies for small-scale digesters. In this study, semi-continuous anaerobic digesters were operated in replicate at four different loading rates (control, 0.3, 0.8 and 1.3 kg VS/m3/day) and housed in an environment that simulated seasonal change (27.5°C,10°C and 27.5°C). The results illustrate that class B quality biosolids were generated for all treatments as per guidelines from the United States Environmental Protection Agency (USEPA). The simulated seasonal change did not influence Escherichia coli or faecal coliform levels, while it did appear to have an effect upon levels of Enterococci. Reduced loading rates led to a more stable environment (in terms of pH, levels of volatile fatty acids (VFAs) and total inorganic carbonate (TIC)) as well as lower levels of indicator bacteria, but generated slightly lower biogas volumes (high – 53.23 L vs. low – 53.19 L) over the course of the study. The results provide important data to improve the performance of small-scale psychrophilic digesters, specifically by reducing loading rates to prevent souring during winter months.

Immobilization of anaerobic bacteria on rubberized-coir for psychrophilic digestion of night soil

Low-ambient temperatures, <30 °C, are known to cause drastic reduction in the efficiency of anaerobic biodigesters due to low-growth rate of the constituent bacterial consortium. Immobilization of anaerobic bacteria has been attempted in the biodigester operating at 10 °C. Various matrices were screened and evaluated for the immobilization of bacteria in digesters. Anaerobic digestion of night soil was carried out with hydraulic retention time in the range of 9–18 days. Among the tested matrices, rubberized-coir was found to be the most useful at 10 °C with optimum hydraulic retention time of 15 days. Optimum amount of coir was found as 25 g/L of the working volume of biodigesters. Immobilization of bacteria on the coir was observed by scanning electron microscopy and fluorescent microscopy. The study indicates that rubberized coir can be utilized to increase biodegradation of night soil at higher organic loading. Another advantage of using this matrix is that it is renewable and easily available in comparison to other synthetic polymeric matrices.

Anaerobic biological treatment of phenolic wastewater at 15–18 °C

Low-temperature, or psychrophilic (<20 °C) anaerobic digestion has been proven feasible for the mineralisation of simple wastewaters. In this study, hybrid expanded granular sludge bed-anaerobic filter (EGSB-AF) bioreactors were used to evaluate the feasibility of psychrophilic digestion for the treatment of phenol-containing wastewater. Efficient chemical oxygen demand and phenol removal were observed at organic and phenol loading rates of 5 kg COD m −3 d −1 and 0.4–1.2 kg phenol m −3 d −1 (400–1200 mg phenol [l wastewater] −1), respectively. There was no long-term accumulation of volatile fatty acids in the reactor systems. Methanogenic activity was developed under psychrophilic conditions but anaerobic methane-producing populations remained mesophilic throughout the trial of 415 days.

Psychrophilic anaerobic digestion of animal manure: Proposed design methodology

A comprehensive literature review was conducted on psychrophilic anaerobic digestion and design of anaerobic digesters for treating animal manures. Anaerobic digestion of caged layer manure was studied in the laboratory at low temperatures (14–23°C). The digesters were operated to determine combinations of temperature and loading rate that gave acceptable methane yield. Acceptable methane yield was obtained for loading rates ranging between 0·15 kg VS/m day and 0·57 kg VS/m 3 day for temperatures of 14°C and 23°C, respectively. The resulting data along with that taken from similar tests documented in the literature was found to approximate the van't Hoff-Arrhenius equation. This equation is then suggested as a technique for determining suitable loading rates for psychrophilic digesters based on data for digesters operated at higher temperatures.

Psychrophilic digestion of dairy cattle and pig manure: Start-up procedures of batch, fed-batch and CSTR-type digesters

Procedures were evaluated to start up anaerobic digesters at psychrophilic temperatures (5–20°C) fermenting either pig or dairy cattle manure. Below 20°C no methane formation was initiated without inoculum. Using a temperature-adapted seed material (50%), batch cultures and accumulation systems could be started at temperatures as low as 5 and 10°C, respectively. Independent of the system, the time to start up cattle manure at 20–25°C took as long as 10–40 days, depending on whether an inoculum was used or not. The corresponding value for pig manure was 40–60 days. In an accumulation system the start-up time of pig manure could be shortened by 20 days when stored cow manure was added. The addition of a 100% seed of mesophilically-treated sludge was a suitable means of initiating digestion of cattle manure in a continuous-flow system at 20°C as long as the retention time remained above 40 days.