Modelling start-up performance of anaerobic digestion of saline-rich macro-algae

Some of the key factors affecting the adaptation of anaerobic digestion processes to increasing levels of salinity were determined in batch tests using brown seaweed as a feedstock. It was found that cultures seeded with non-saline anaerobic inoculum required an adaptation period of up to two months to reach the same level of methane production rate as in those cultures seeded with saline adapted inoculum. The anaerobic digestion model N.1 (ADM1) was modified to include an extra inhibition function to account for the effect of salinity and calibrated using a set of experimental data obtained from batch biochemical methane potential tests. After calibration, the model was able to accurately predict methane production rates. The results thus show that, in the absence of saline-adapted inoculum, non-saline inoculum can be used for the start-up of anaerobic digestion systems treating saline-rich feedstocks

Reviewing factors affecting the effectiveness of decentralised domestic wastewater treatment systems for phosphorus and pathogen removal

Environmental pollution and risks to human health can result from diffuse sources of pollution originating from decentralised wastewater treatment systems (DWTS). In particular phosphorus pollution can lead to eutrophication and the downgrading of the quality of water bodies, for example, under the Water Framework Directive (WFD) in the EU, and pathogen pollution can result in increased risks of human exposure to pathogens and impacts on industries such as shellfish growing and tourism. The study reported in this paper reviews the effectiveness of various DWTS in removing phosphorus and pathogens from onsite systems. It was found that DWTS are typically not designed to specifically treat these pollutants and the most common type of DWTS, septic tanks, provide only basic treatment. Additional treatment such as filtration-based or wetland systems must be used to achieve desired levels of treatments. The performance of these systems is affected by site specific conditions, such as input load and sources, and climatic conditions and as such operational characteristics and treatment measures must be designed to take account of these factors

Hydrolytic effects of acid and enzymatic pre-treatment on the anaerobic biodegradability of <i>Ascophyllum nodosum</i> and <i>Laminaria digitata</i> species of brown seaweed

Abundant marine biomass in coastal regions has continued to attract increasing attention in recent times as a possible source of renewable energy. This study aimed to evaluate the effects of hydrolytic pre-treatment for the purpose of enhancing biogas yield of Laminaria digitata and Ascophyllum nodosum species found on the west coast of Scotland. Results show that L. digitata, in its natural and untreated form, appears to be more readily hydrolysable than A. nodosum. Two treatments were assessed: acid only and acid followed by enzyme. Both treatments enhanced the hydrolysis of both seaweed species, with acid-enzyme treatment providing a better performance

Municipal wastewater treatment and associated bioenergy generation using anaerobic granular bed baffled reactor

This study assesses a modified anaerobic granular bed baffled reactor (GRABBR) which was assessed for municipal wastewater treatment at high organic loading rates (chemical oxygen demand ≥ 1,100 mg/l) under varying temperatures. For the two mesophilic temperatures tested (37⁰C and 25⁰C) under steady state conditions, the removal of Chemical OxygenDemand (COD) and Biochemical Oxygen Demand (BOD) was 80 to 90 %. At lower organic loadings, the reactor operated as a completely mixed system with most of the treatment occurring in the first two compartments. The GRABBR also showed very high solids retention with low effluent suspended solids concentration for all organic and hydraulic conditions. Applications ofGRABBR as a single unit, two-phase treatment system could be an economical option reducing the cost to achieve similar treatment goals for high strength wastewaters. The findings of this research suggest that the application of GRABBR is suitable for the treatment of multiple pollutants present in wastewater where each compartment acts as a specialised treatment stagewith biogas production

Effect of liquid nitrogen pre-treatment on various types of wool waste fibres for biogas production

This study investigated the role of liquid nitrogen (LN2) in increasing microbial accessibility of wool proteins for biogas production. It involves a mechanical size reduction of four different types of raw wool fibres, namely, Blackface, Bluefaced Leicester, Texel and Scotch Mule, in presence of liquid nitrogen, followed by the determination of the methane production potential of the pre-treated wool fibres. The highest methane yield, 157.3 cm3 g−1 VS, was obtained from pre-treated Scotch mule wool fibre culture, and represented more than 80% increase when compared to the yield obtained from its raw equivalent culture. The increase in biogas yield was attributed to the effectiveness of LN2 in enhancing particle size reduction and the consequent increase in wool solubility and bioavailability. Results also showed that LN2 pre-treatment can enhance size reduction but has limited effect on the molecular structure. The study also showed that the biogas potential of waste wool fibres varies with the type and source of wool

Ethanol production from brown seaweed using non-conventional yeasts

The use of macroalgae (seaweed) as a potential source of biofuels has attracted considerable worldwide interest. Since brown algae, especially the giant kelp, grow very rapidly and contain considerable amounts of polysaccharides, coupled with low lignin content, they represent attractive candidates for bioconversion to ethanol through yeast fermentation processes. In the current study, powdered dried seaweeds (Ascophylum nodosum and Laminaria digitata) were pre-treated with dilute sulphuric acid and hydrolysed with commercially available enzymes to liberate fermentable sugars. Higher sugar concentrations were obtained from L. digitata compared with A. nodosum with glucose and rhamnose being the predominant sugars, respectively, liberated from these seaweeds. Fermentation of the resultant seaweed sugars was performed using two non-conventional yeast strains: Scheffersomyces (Pichia) stipitis and Kluyveromyces marxianus based on their abilities to utilise a wide range of sugars. Although the yields of ethanol were quite low (at around 6 g/L), macroalgal ethanol production was slightly higher using K. marxianus compared with S. stipitis. The results obtained demonstrate the feasibility of obtaining ethanol from brown algae using relatively straightforward bioprocess technology, together with non-conventional yeasts. Conversion efficiency of these non-conventional yeasts could be maximised by operating the fermentation process based on the physiological requirements of the yeasts

Assessment of leachable and persistent dissolved organic carbon in sludges and biosolids from municipal wastewater treatment plants

Environmental regulation of organic pollutants has not kept pace with the growth in the number and diversity of legacy and emerging organic substances now in use. Simpler and cheaper tools and methodologies are needed to quickly assess the organic pollutant risks in waste materials applied to land such as municipal wastewater treatment sludges and biosolids. This study attempts to provide these, using an approach that consists of chemical leaching and analysis of dissolved organic carbon and determination of its biodegradability by measuring persistent dissolved organic carbon. Primary and secondary sludges, dewatered sludge cake, and anaerobically and thermally treated biosolids obtained from various types of municipal wastewater treatment plants were used in the study. The study found little variability in the levels of dissolved organic carbon leached from primary sludges obtained from different municipal wastewater treatment plants but found significant differences for secondary sludges based on levels of nitrification at the municipal wastewater treatment plants. As predicted treated biosolids leached less dissolved organic carbon than untreated dry sludges but had relatively higher proportions of persistent or poorly biodegradable dissolved organic carbon. Across all tested sludges and biosolids persistent dissolved organic carbon ranged from 14 to 39%, with biosolids that have undergone anaerobic digestion and thermal treatment more likely to contain greater relative proportion of persistent dissolved organic carbon than untreated sludges. The approach presented in this study will be useful in assessing the effectiveness of current and widely employed sludge treatment methods in reducing persistent organic pollutants in biosolids disposed on land

Co-digestion of terrestrial plant biomass with marine macro-algae for biogas production

This paper investigates factors affecting anaerobic degradation of marine macro-algae (or seaweed), when used as a co-substrate with terrestrial plant biomass for the production of biogas. Using Laminaria digitata, a brown marine seaweed species and green peas, results showed that when only 2% of feedstock of a reactor treating the green peas at an organic loading rate (OLR) of 2.67 kg VS.m3.day-1 was replaced with the seaweed, methane production was disrupted, whilst acidogenesis, seemed to be less adversely affected, resulting in excessive volatile acids accumulation. Reactor stability was difficult to achieve thereafter. The experiment was repeated with a lower initial OLR of green peas of 0.70 kg VS.m3.day-1 before the addition of the seaweed. Although similar symptoms as in first trial were observed, process stability was restored through the control of OLR and alkalinity. These measures led to an increase in overall OLR of 1.25 kg VS.m3.day-1 comprising of 35% seaweed. This study has shown that certain seaweed constituents are more inhibitory to the methanogens even at trace concentrations than to the other anaerobic digestion microbial groups. Appropriate adaptation strategy, involving initial low proportion of the seaweed relative to the total OLR, and overall low OLR, is necessary to ensure effective adaptation of the microorganisms to the inhibitory constituents of seaweed. Where there is seasonal availability of seaweed, the results of this study suggest that a fresh adaptation or start-up strategy must be implemented during each cycle of seaweed availability in order to ensure sustainable process stability

Road deposited sediment:implications for the performance of filter drains servicing strategic trunk roads

This study investigates the contribution of road deposited sediment (RDS) to clogging and the operational lifecycle of Highway Filter Drains (HFDs). RDS samples were collected from 9 Scottish trunk roads and fractionated into grain size classes to determine their particle size distributions (PSD). Results show that RDS PSDs, and the percentage of each grain size fraction, are highly variable. However, despite being collected from different trunk roads, PSD trends are similar, with individual RDS particles ranging in size from &lt;63 μm to &gt;10,000 μm. Medium sand, coarse sand, fine gravel and medium gravel make up 84.1% of the total particle mass concentration, with particles &gt;1,000 μm mostly mineral or asphalt. The study also reveals that the dynamic nature of a trunk road catchment dictates that grading envelopes are essentially instantaneous values. These findings indicate that large particles from the road surface, contribute to clogging and have the potential to reduce the operational lifecycle of HFDs. The study also demonstrated that assuming a single RDS PSD profile for filter drain asset management purposes is unlikely to be representative of a trunk road catchment profile

Effects of thermo-chemical and enzymatic pre-treatment of tropical seaweeds and freshwater macrophytes on biogas and bioethanol production

The use of aquatic biomass as potential sources for bioenergy production has attracted significant attention worldwide. Production of biogas and bioethanol from both marine and freshwater plants using same pre-treatment methods were evaluated and the results indicate that both processes can be potentially enhanced appropriate methods of pre-treatment. In this study, the effects of thermochemical and enzymatic pre-treatment of selected seaweeds and freshwater macrophytes for biogas and bioethanol production were investigated. It was found that methane biogas yield from the anaerobic digestion of selected aquatic plants was highly dependent on the plant species. For example, biomethane yields of 189, 195, 221, 234 mL/g volatile solids were obtained following anaerobic digestion of acid and enzymatic pre-treatment of Laminaria digitata, Sargassum fluitans, Eichhornia crassipies and Pistia stratiotes, respectively. Additionally, alcoholic fermentation by the yeast Saccharomyces cerevisiae (distiller’s strain) was carried out on aquatic plant hydrolysates and the highest ethanol yields (of over 4 g/L) were obtained from Eichhornia crassipies and Pistia stratiotes. Poor fermentation yields from Laminaria digitata, and Sargassum fluitans hydrolysates were attributed to the predominance of un-fermented rhamnose sugars in these plants. The findings demonstrate the importance of reliance on empirical data for each substrate when designing and operating anaerobic digestion and alcohol fermentation systems. The results show that the same pre-treatment methods can be used for both types of bioenergy production, i.e., biogas and bioethanol, from marine and freshwater plants, thereby enhancing the economic viability of both processes in industry-scale applications.</p