Carbon footprint of dairy manure management chains in response to nutrient recovery by aerobic pre-treatment.

Aerobic pre-treatment of liquid dairy manure has previously been reported as an effective nutrient export and emissions mitigation approach. The first objective of this study was to experimentally determine the optimal intermittent aeration ratio for nutrient recovery from liquid dairy manure through an on-site pilot-scale reactor to partially reduce the required energy for the aerobic process. The second objective was to theoretically investigate the total carbon footprints of direct manure spreading on croplands and permanent manure storage in open anaerobic lagoons in response to nutrient removal by the optimal determined intermittent aerobic treatment ratio. Four scenarios (S) were included; S1 was the traditional scenario of manure spread on croplands without the aerobic pre-treatment, S2 was the modified scenario of manure spread on croplands that included the aerobic pre-treatment, S3 was the traditional scenario of manure storage in lagoons, and S4 was the modified scenario of manure storage in lagoons that included the aerobic pre-treatment. The results showed that comparable nutrient removal efficiencies could be obtained with a 5:1 intermittent aeration ratio. Total nitrogen (TN) and total phosphorus (TP) were recovered were 41.5 ± 1.3% and 37.0 ± 4.0%, respectively, in ammonium sulfate and phosphorus-rich sludge, while 55.3 ± 1.4% of the chemical oxygen demand (COD) was removed. The estimated total carbon footprint for S1, S2, S3, and S4 were 24.4, 37.9, 45.3, and 45.9 kg CO2-eqton-1, respectively. However, the total carbon footprint of S2' and S4', which used renewable-based energy to run the reactor instead of fossil-based energy used in S2 and S4, were estimated to 29.5 and 37.5 kg CO2-eqton-1, respectively. Clearly, applying the aerobic pre-treatment increased the total carbon footprint of all cases except S4', in which the total carbon footprint was mitigated by -17.2%. Accordingly, the aerobic pre-treatment is only recommended in the case of S4' from a carbon footprint point of view although it is an effective nutrient recovery technology.

Response of phosphorus speciation to organic loading rates and temperatures during anaerobic co-digestion of animal manures and wheat straw.

The world is facing huge phosphate (P) shortage and anaerobic digestion (AD) is a recognized technology to promote nutrient (N and P) recycling. The composition of P speciation in the digestate is essential for the fertilizing effect. However, how P speciation in the digestates interacts with the AD process conditions is unknown. Therefore, interaction of P speciation in digestates with AD process conditions was investigated by using a chemical sequential extraction method (Hedley fractionation) and X-ray diffraction; specifically, the effects of organic loading rate (OLR), temperature, and substrate composition were investigated. The results showed that OLR and feedstock affected P speciation in the digestate significantly due to different ion species and ionic strengths. The H2O-P concentration in chicken manure with straw (CMS) and dairy manure with straw (DMS) digestates decreased by 44.04-48.76% and 48.88-50.49%, respectively, as the OLR increased from 2 to 4 kg VS m-3 d-1. Simultaneously, HCl-P increased by 38.02-44.01% in the CMS digestates due to Ca-P and Mg-P formation, indicating that Ca-P and Mg-P formation was positively correlated with OLR, whereas P mobility decreased. Further, thermophilic temperature conditions were more conducive for the formation of insoluble P than mesophilic temperature conditions in the digestates due to the thermodynamic driving force of the reactions. The results would facilitate the understanding of P transformation in the AD process under the influence of feedstock, OLR, and temperature. From the viewpoint of nutrient management, lower OLR and temperature are more beneficial for a fast P availability, whereas higher OLR and temperature are more helpful for storage and export because of P precipitated into solid phase of digestate.

Effect of design and operational parameters on nutrients and heavy metal removal in pilot floating treatment wetlands with Eichhornia Crassipes treating polluted lake water.

Though having an economic and ecological impact on Marriott Lake management in Egypt, water hyacinth (Eichhornia crassipes) is an aquatic floating macrophyte with a known phytoremediation potential. In order to assess its remediation potential, pilot floating treatment wetlands (FTWs) with E. crassipes were built in duplicates to evaluate the removal of nutrients and heavy metals from the polluted lake water. The experimental design included units with different water depths (15, 25, and 35 cm; D15, D25, and D35, respectively) and plant coverage (90, 70, 50, and 0%; P90, P70, P50, and P0, respectively). The pilot FTWs were monitored over a 7-day operation cycle to identify the optimum combination of design (plant coverage, water depth) and operation (hydraulic retention time; HRT) parameters needed for maximum BOD5, TN, NH4-N, and TP removal. NH4-N removal reached 97.4% in the D25P50 unit after 3 days, BOD5 75% in the D15P90 after 3 days, TN 82% in the D25P70 after 4 days, and TP 84.2% in the D35P70 after 4 days. The open-water evaporation rate was higher than the evapotranspiration rate in the planted units, probably due to the warm climate of the study area. Metals were also sufficiently removed through bioaccumulation in plant tissues in the order of Fe > Pb > Cu > Ni (62.5%, 88.9%, 81.7%, and 80.4% for D25P50, D25P70, D25P50, and D25P90, respectively), while most of the assimilated metal mass was translocated to the plant roots. The biochemical composition of the plant tissue was significantly different between the shoot and root parts. Overall, the FTW with 70% E. crassipes coverage, 25-cm water depth, and an HRT of 3-5 days was identified as the optimum design for effective remediation of the polluted Marriott Lake in Egypt.

Influence of anaerobic digestion on the labile phosphorus in pig, chicken, and dairy manure.

Phosphorus (P) loss from livestock and poultry industry causes serious threat to agro-ecological environments. Anaerobic digestion (AD), through recycling of P-containing resources and biogas production, prevails as a promising solution to the resource, energy, and environment trilemma. In this study, the dynamic transformation of P in batch AD processes fed with chicken, pig and dairy manures was investigated. Results showed that the Labile-P of total phosphorus (TP) in pig, chicken and dairy manure digestates decreased from 37.35% to 23.79%, 36.79% to 17.29%, and 60.47% to 20.39%, respectively, and was associated with an increase of NaOH-P during the AD process. However, the Labile-P in raw manures ranging from 64.67% to 81.10%, indicated that AD could reduce the pollution risk caused by the overuse of high Labile-P animal manure as fertilizer. Metal ions had a significant influence on P transformation because of their ability to combine with PO43-/HPO42-. During AD, the species of phosphates increased: AlPO4, FePO4, Mg3(PO4)2, CaHPO4, Mg(NH4)PO4·6H2O and Ca10(PO4)6(OH)2 were the main phosphates qualified by X-ray diffraction (XRD). AD produced a satisfactory fertilizer for plants that were able to activate the precipitated P, which could provide readily available N and slow-release P. This study provides a meaningful theoretical guide for recycling P from animal manure resources.