The role of microbial ecology in improving the performance of anaerobic digestion of sewage sludge

The use of next-generation diagnostic tools to optimise the anaerobic digestion of municipal sewage sludge has the potential to increase renewable natural gas recovery, improve the reuse of biosolid fertilisers and help operators expand circular economies globally. This review aims to provide perspectives on the role of microbial ecology in improving digester performance in wastewater treatment plants, highlighting that a systems biology approach is fundamental for monitoring mesophilic anaerobic sewage sludge in continuously stirred reactor tanks. We further highlight the potential applications arising from investigations into sludge ecology. The principal limitation for improvements in methane recoveries or in process stability of anaerobic digestion, especially after pre-treatment or during co-digestion, are ecological knowledge gaps related to the front-end metabolism (hydrolysis and fermentation). Operational problems such as stable biological foaming are a key problem, for which ecological markers are a suitable approach. However, no biomarkers exist yet to assist in monitoring and management of clade-specific foaming potentials along with other risks, such as pollutants and pathogens. Fundamental ecological principles apply to anaerobic digestion, which presents opportunities to predict and manipulate reactor functions. The path ahead for mapping ecological markers on process endpoints and risk factors of anaerobic digestion will involve numerical ecology, an expanding field that employs metrics derived from alpha, beta, phylogenetic, taxonomic, and functional diversity, as well as from phenotypes or life strategies derived from genetic potentials. In contrast to addressing operational issues (as noted above), which are effectively addressed by whole population or individual biomarkers, broad improvement and optimisation of function will require enhancement of hydrolysis and acidogenic processes. This will require a discovery-based approach, which will involve integrative research involving the proteome and metabolome. This will utilise, but overcome current limitations of DNA-centric approaches, and likely have broad application outside the specific field of anaerobic digestion

Potassium releasing and supplying power of selected yellow grey earth soils of New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University

The supply of soil potassium (K) to New Zealand pastures is currently being assessed by the quick test K (QTK) and reserve K (Kc) methods, which measure soil exchangeable K (Kex) and non-exchangeable K (Knex), respectively. QTK is based on a routine soil test and Kc is an assigned estimate appropriate to the soil group. No consideration is given to the variations of the Knex supply within a soil group. The objective of this research was to examine the K releasing and K supplying power of selected soils from the yellow-grey earth (YGE) group. A wide variation was observed in the measured Kc values of the YGE soils in the North and South Islands. A glasshouse experiment showed that the supply of Knex to ryegrass grown on the 13 North Island YGE soils ranged from 0-41 mg 100 g-1 and that of the 6 South Island YGE soils ranged from 3-35 mg 100 g-1. The experiment also showed that there were lower levels of Knex supply in the pasture sites, compared to the virgin sites with respect to the South Island YGE soils. These results have implications to the use of the soil group concept which is used to estimate Knex supply in the Computerised Fertilizer Advisory Service (CFAS) K model, currently used by AgResearch. In a laboratory study, the threshold K levels in terms of K concentration and the activity ratio in the equilibrated soil solution, Kex, and the amount of specifically held K were determined, in order to explain the variations in Knex, supply. The threshold K levels were not related to the Knex release and supply. The uptake of K by ryegrass was at best poorly to moderately correlated with the K extracted by current methods of determining K releasing power viz, QTK and Kc. The highest simple correlation was obtained from an improved acid-extractable K procedure (r = 0.96; P < 0.01). The differences in the Knex uptake by ryegrass from various soils were better explained by a simple method of determining soil Knex i.e., step K, than by the existing Kc method. A multiple regression equation with QTK and step K as independent variables explained 96 % of the variation in total K uptake among soils. On the basis of Knex taken up by ryegrass in the glasshouse experiment, the 19 soils in this study were broadly grouped into two categories (i) soils with step K values of less than 35 mg 100 g-1 and a Kc range of 8-10 mg 100 g-1 and (ii) soils with step K values greater than 35 mg 100 g-1 and a Kc range of 12-19 mg 100 g-1. Selected soils were fractioned into sand, silt, and clay separates and acid-extractable K levels of the fractions were measured. There was a wide range in the acid-extractable K levels among the soils for the same size fraction e.g., clay, and for different size fractions within the same soil. When weighted according to the particle size distribution of the soil, the sand was found to contribute 4-45 %, silt 10-40 %, and clay 15-85 % of the K released by the sum of the 3 separates, using the improved acid extraction method. In all the soils, the clay separate released the most K per unit weight. An agar pot trial technique was developed to measure the K supplying power of the soil separates. Although on a unit weight basis the clay separates showed a much greater activity than the other separates on a weighted basis, the contributions of sand and silt separates to the total K uptake of Marton (38 %), Matapiro (41 %), and Wharekaka (25 %) soils was of considerable importance. The results demonstrated that the role of sand and silt separates deserve more consideration in estimating potential K releasing and supplying power than has hitherto been the case. The study also attempted to relate Knex release and supply to the soil mineralogy. Although the gross mineralogy of the 19 soils was similar, differences in the Knex release and supply could be related to subtle differences and gradual changes in the clay mineralogy. The XRD patterns of the clays with a Kc range of 8-10 mg 100 g-1 of soil differed from those with a Kc range of 12-19 mg 100 g-1 of soil. The latter group of clays contain more K bearing minerals than the former group. The practical implications of the measured differences in Kc values (Knex supply) within the YGE soil group were dealt with. The measured Knex supply in the North Island YGE soils ranged from 20-40 kg ha-1 yr-1, whereas the expected Knex supply based on an assigned Kc value is 30 kg ha-1 yr-1. The difference between the expected and the measured Knex may be sufficiently economically significant as to invalidate applying a single Kc value to a soil group. Possible improvements to the soil K supply component of the CFAS K model were suggested, particularly that step K values should replace Kc in the K supply model

Uptake, accumulation, and toxicity of per- and polyfluoroalkyl substances in Allium cepa grown in soils amended with biosolids

Uptake and accumulation of per- and polyfluoroalkyl substances (PFAS) in Allium cepa from soils amended with biosolids were investigated. The Ʃ38 PFAS concentrations in soils amended with biosolids ranged from 10.4 to 104 ng g−1 (dry-weight). Among PFAS, perfluorooctanesulfonate (PFOS) concentration was the highest in soils, with a maximum of 48.1 ng g−1, followed by N-ethylperfluoro-1-octanesulfonamidoacetic acid (N-Et-FOSAA) with the maximum of 10.9 ng g−1. The concentration of perfluorooctanoate (PFOA) was higher (0.55–1.82 ng g−1) in roots of A. cepa than that of PFOS (0.03–0.13 ng g−1). The accumulation of PFAS in A. cepa shoots depended on the carbon chain length, with a more significant accumulation of shorter C-chain PFAS than the longer C-chain derivatives. The concentration of PFAS in shoots correlated positively with corresponding root concentration, suggesting a significant translocation of PFAS from root to shoots. A. cepa showed no considerable cyto-genotoxicity in the meristem root tip cells exposed to soils amended with biosolids. The oxidative stress parameters such as reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and lipid peroxidation (LP) showed no significant change over control in A. cepa root cells exposed to soils amended with biosolids. The estimated dietary intake for PFOA and PFOS did not exceed the recommended tolerable daily intake (TDI) even after assuming that onion accounted for 100% of vegetable consumption. This study provides evidence of accumulation and translocation of PFAS from soil to roots and shoots of A. cepa. Also, we assessed the potential risk of PFAS accumulated in A. cepa to humans via the food chain to be insignificant

Wood Biochar Enhances the Valorisation of the Anaerobic Digestion of Chicken Manure

In this study, the efficacy of biochar to mitigate ammonia stress and improve methane production is investigated. Chicken manure (CM) was subjected to high-solid mesophilic anaerobic digestion (15% total solid content) with wood biochar (BC). Wood biochar was further treated using HNO3 and NaOH to produce acid–alkali-treated wood biochar (TBC), with an improvement in its overall ammonium adsorption capacity and porosity. Three treatments were loaded in triplicate into the digesters, without biochar, with biochar and with acid–alkali-treated biochar and maintained at 37 °C for 110 days. The study found a significant improvement in CH4 formation kinetics via enhanced substrate degradation, leading to CH4 production of 74.7 mL g−1 VS and 70.1 mL g−1 VS by BC and TBC treatments, compared to 39.5 mL g−1 VS by control treatments on the 28th day, respectively. However, only the use of TBC was able to prolong methane production during the semi-inhibition phase. The use of TBC also resulted in the highest removal of total ammonia nitrogen (TAN) of 86.3%. In addition, the treatment with TBC preserved the highest microbial biomass at day 110. The presence of TBC also resulted in an increase in electrical conductivity, possibly promoting DIET-mediated methanogenesis. Overall, the acid–alkali treatment of biochar can be a novel approach to improve biochar’s existing characteristics for its utilisation as an additive in anaerobic digestion

Detection of Helminth Ova in Wastewater Using Recombinase Polymerase Amplification Coupled to Lateral Flow Strips

Ascaris lumbricoides is a major soil-transmitted helminth that is highly infective to humans. The ova of A. lumbricoides are able to survive wastewater treatment, thus making it an indicator organism for effective water treatment and sanitation. Hence, Ascaris ova must be removed from wastewater matrices for the safe use of recycled water. Current microscopic techniques for identification and enumeration of Ascaris ova are laborious and cumbersome. Polymerase chain reaction (PCR)-based techniques are sensitive and specific, however, major constraints lie in having to transport samples to a centralised laboratory, the requirement for sophisticated instrumentation and skilled personnel. To address this issue, a rapid, highly specific, sensitive, and affordable method for the detection of helminth ova was developed utilising recombinase polymerase amplification (RPA) coupled with lateral flow (LF) strips. In this study, Ascaris suum ova were used to demonstrate the potential use of the RPA-LF assay. The method was faster (&lt; 30 min) with optimal temperature at 37 &deg;C and greater sensitivity than PCR-based approaches with detection as low as 2 femtograms of DNA. Furthermore, ova from two different helminth genera were able to be detected as a multiplex assay using a single lateral flow strip, which could significantly reduce the time and the cost of helminth identification. The RPA-LF system represents an accurate, rapid, and cost-effective technology that could replace the existing detection methods, which are technically challenged and not ideal for on-site detection in wastewater treatment plants

A modified approach to recover and enumerate Ascaris ova in wastewater and sludge.

A modified approach to recover and enumerate <i>Ascaris</i> ova in wastewater and sludg