The increasing population creates excess pressure on the plantation and production of fruits and vegetables across the world. Consumption demand during the whole year has made production compulsory in the covered production system (greenhouse). Production, harvesting, processing, transporting, and distribution chains of fruit and vegetables have resulted in a huge amount of wastes as an alternative source to produce biofuels. In this study, optimization of two pretreatment processes (NaOH and HCl assisted thermal) was investigated to enhance methane production from fruit and vegetable harvesting wastes (FVHW) that originate from greenhouses. NaOH concentration (0–6.5%), HCl concentration (0–5%), reaction temperature (60–100 °C), solid content (1–5%), time of reaction (1–5 h), and mixing speed (0–500 rpm) were chosen in a wide range of levels to optimize the process in a broad design boundary and to evaluate the positive and negative impacts of independent variables along with their ranges. Increasing NaOH and HCl concentrations resulted in higher COD solubilization but decreased the concentration of soluble sugars that can be converted directly into methane. Thus, the increasing concentrations of NaOH and HCl in the pretreatments have resulted in low methane production. The most important independent variables impacting COD and sugar solubilization were found to be chemical concentration (as NaOH and HCl), solid content and reaction temperature for the optimization of pretreatment processes. The high amount of methane productions in the range of 222–365 mL CH4 gVS−1 was obtained by the simple thermal application without using chemical agents as NaOH or HCl. Maximum enhancement of methane production was 47–68% compared to raw FVHW when 5% solid content, 1-hour reaction time and 60–100 °C reaction temperature were applied in pretreatments.

中文翻译：

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化学辅助热预处理对水果和蔬菜收获废物产生甲烷的影响：工艺优化

不断增长的人口对世界各地的水果和蔬菜的种植和生产造成了过大的压力。全年的消费需求使覆盖的生产系统（温室）强制生产。水果和蔬菜的生产、收获、加工、运输和分销链产生了大量废物，作为生产生物燃料的替代来源。在这项研究中，研究了两种预处理工艺（NaOH 和 HCl 辅助热）的优化，以提高源自温室的水果和蔬菜收获废物 (FVHW) 的甲烷产量。NaOH 浓度 (0–6.5%)、HCl 浓度 (0–5%)、反应温度 (60–100 °C)、固含量 (1–5%)、反应时间 (1–5 h)、和混合速度 (0–500 rpm) 被选择在广泛的水平范围内，以在广泛的设计边界内优化过程，并评估自变量及其范围的正面和负面影响。增加 NaOH 和 HCl 浓度会导致更高的 COD 溶解，但会降低可直接转化为甲烷的可溶性糖的浓度。因此，预处理中 NaOH 和 HCl 浓度的增加导致甲烷产量降低。发现影响 COD 和糖溶解的最重要的自变量是化学浓度（如 NaOH 和 HCl）、固体含量和用于优化预处理过程的反应温度。在 222–365 mL CH4 gVS-1 范围内的大量甲烷产量是通过简单的热应用获得的，而无需使用 NaOH 或 HCl 等化学试剂。当在预处理中应用 5% 的固含量、1 小时的反应时间和 60-100 °C 的反应温度时，与原始 FVHW 相比，甲烷产量的最大提高为 47-68%。